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Tom Kyte

Thanks for the question, ali.

Asked: July 20, 2000 - 3:05 am UTC

Answered by: Tom Kyte - Last updated: August 03, 2020 - 2:29 pm UTC

Category: Database - Version: oracle 8.0.5

Viewed 100K+ times! This question is

You Asked

how can i create database links to access remote databases.
please tell me the procedure of creating database links.


and we said...

You need a tnsnames entry in your tnsnames.ora on the server. If you can:

sqlplus scott/tiger@some_other_database

from the machine the server you want to create the database link ON works -- you've gotten the first step done.

For example, I can:

$ sqlplus scott/tiger@ora8idev

SQL*Plus: Release 8.1.5.0.0 - Production on Thu Jul 20 09:16:25 2000
(c) Copyright 1999 Oracle Corporation. All rights reserved.
Connected to:
Oracle8i Enterprise Edition Release 8.1.5.0.0 - Production
With the Partitioning and Java options
PL/SQL Release 8.1.5.0.0 - Production
scott@DEV8I.WORLD>


Once you have that setup, you log into the database (the local database -- the one you want to create the database link in to connect to the OTHER database) and issue the create database link command (see the sql reference manual for complete syntax). For example I can:



scott@8i> create database link ora8idev
2 connect to scott
3 identified by tiger
4 using 'ora8idev'
5 /

Database link created.

scott@8i> select * from dual@ora8idev;

D
-
X

scott@8i>

I do not have to use the connect to and identified by clauses, if I do not, it will use the login and password of the currently connected user to connect to the remote database.



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Is this answer out of date? If it is, please let us know via a Review

Reviews

tnsnames

March 10, 2002 - 4:24 am UTC

Reviewer: mohammad toaha from Dubai, UAE

My problem description is detailed below:


SQL>  CONNECT DEWADBA/DEWADBA      -- Connected to local database
Connected.
SQL>  CREATE TABLE T12 AS SELECT * FROM W_NODE@DISPDC;
 CREATE TABLE T12 AS SELECT * FROM W_NODE@DISPDC
                                          *
ERROR at line 1:
ORA-02019: connection description for remote database not found


SQL> CREATE TABLE T12 AS SELECT * FROM W_NODE@DISPDC;
CREATE TABLE T12 AS SELECT * FROM W_NODE@DISPDC
                                         *
ERROR at line 1:
ORA-02019: connection description for remote database not found

SQL> CONNECT DEWADBA/DEWADBA@DISPDC         -- connected to remote database
Connected.

Then,as an alternative, I tried to cretae a database link as below:

SQL> create database link dispdc1
  2  connect to dewadba identified by dewadba98
  3  using 'dispdc';

Database link created.

SQL> connect dewadba/dewadba
Connected.
SQL> create table t12 as select * from w_node@dispdc1;
create table t12 as select * from w_node@dispdc1
                                         *
ERROR at line 1:
ORA-02085: database link DISPDC1.world connects to ORACLE.WORLD

- I worked around the tnsnames.ora file in various ways but could not succeed. 

Tom Kyte

Followup  

March 10, 2002 - 6:30 pm UTC

search for ora-02085 on this site and you'll see what needs be done for that.

For the first problem, the ora-02019 - you don't have a DATABASE LINK yet, so I would not expect that to work.

How to create synonym for a database link

September 07, 2002 - 2:55 am UTC

Reviewer: Suresh&kanagaraj from Chennai

Hi Tom,
   I have created a dblink as follows
  create PUBLIC database link ORACLE.US.ACME.COM
  connect to scott
  identified by tiger
  using 'VINSERVER'

 select * from emp@ORACLE.US.ACME.COM
 /

 EMPNO ENAME      JOB              MGR HIREDATE         SAL       COMM
------ ---------- --------- ---------- --------- ---------- ----------
DEPTNO
------
  7369 SMITH      CLERK           7902 17-DEC-80        800
    20

  7499 ALLEN      SALESMAN        7698 20-FEB-81       1600        300
    30

  7521 WARD       SALESMAN        7698 22-FEB-81       1250        500
    30

Then i have created a synonym for this database link as follows

  1* create PUBLIC synonym syn_oracle for emp@ORACLE.US.ACME.COM
SQL> /

Synonym created.

Now when i describe the synonym i get the following error

SQL> DESC SYN_ORACLE;
ERROR:
ORA-02019: connection description for remote database not found

Can you pls help

Thanks
Suresh&Kanagaraj

 

Tom Kyte

Followup  

September 07, 2002 - 10:35 am UTC

describe doesn't always work over a DBLINK.

My *preferred* method for doing this is:

create view V as select * from emp@whereever;


That has the added benefit that the metadata for V is pulled into our local database (eg: you can select * from user_tab_columns where table_name = 'V' for example). More applications -- specially ones that rely on the data dictionary -- can use V this way then if V was a public synonym (and I'm not very fond of public synonyms in GENERAL -- they have performance implications and more importantly -- they polute the namespace, leading to issues with more then one application in a database. What happens when app1 has an EMP table ana so does app2? Who gets the public synonym? I rarely use them)

time out tns

February 04, 2003 - 11:03 am UTC

Reviewer: Marcio from Brazil

Tom, What is wrong?

sre_d@SISNUM8I> exec print_table ( 'select * from user_db_links' );
DB_LINK : MRP.AQUARIUS.CPQD.COM.BR
USERNAME : SCOTT
PASSWORD : TIGER
HOST : mrp
CREATED : 04-feb-2003 13:50:59
-----------------

PL/SQL procedure successfully completed.

sre_d@SISNUM8I> select * from global_name;

GLOBAL_NAME
----------------------------------------------------------------------
SISNUM8I.AQUARIUS.CPQD.COM.BR

sre_d@SISNUM8I> select * from dual@mrp;
select * from dual@mrp
*
ERROR at line 1:
ORA-12535: TNS:operation timed out


sre_d@SISNUM8I> alter session set global_names = false;

Session altered.

sre_d@SISNUM8I> select * from dual@mrp;
select * from dual@mrp
*
ERROR at line 1:
ORA-12535: TNS:operation timed out


sre_d@SISNUM8I> alter session set global_names = true;

Session altered.

sre_d@SISNUM8I> select * from dual@mrp;
select * from dual@mrp
*
ERROR at line 1:
ORA-12535: TNS:operation timed out

sre_d@SISNUM8I>
sre_d@SISNUM8I> @conn scott/tiger@mrp
scott@MRP816>


C:\Oracle\Ora81\network\ADMIN>type sqlnet.ora
# SQLNET.ORA Network Configuration File: c:\Oracle\Ora81\network\admin\sqlnet.ora
# Generated by Oracle configuration tools.

# NAMES.DEFAULT_DOMAIN = aquarius.cpqd.com.br

SQLNET.AUTHENTICATION_SERVICES= (NTS)

NAMES.DIRECTORY_PATH= (TNSNAMES, ONAMES, HOSTNAME)


C:\Oracle\Ora81\network\ADMIN>type tnsnames.ora
# TNSNAMES.ORA Network Configuration File: c:\Oracle\Ora81\network\admin\tnsnames.ora
# Generated by Oracle configuration tools.

EXTPROC_CONNECTION_DATA.AQUARIUS.CPQD.COM.BR =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
(CONNECT_DATA =
(SID = PLSExtProc)
(PRESENTATION = RO)
)
)

mrp =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = CPQD020496)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = mrp816)
)
)


sre =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = CPQD050068)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = SISNUM8I)
)
)
C:\Oracle\Ora81\network\ADMIN>type listener.ora
# LISTENER.ORA Network Configuration File: c:\Oracle\Ora81\network\admin\listener.ora
# Generated by Oracle configuration tools.

LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC0))
)
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = CPQD020496)(PORT = 1521))
)
)
(DESCRIPTION =
(PROTOCOL_STACK =
(PRESENTATION = GIOP)
(SESSION = RAW)
)
(ADDRESS = (PROTOCOL = TCP)(HOST = CPQD020496)(PORT = 2481))
)
)

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SID_NAME = PLSExtProc)
(ORACLE_HOME = c:\Oracle\Ora81)
(PROGRAM = extproc)
)
(SID_DESC =
(GLOBAL_DBNAME = mrp816)
(ORACLE_HOME = c:\Oracle\Ora81)
(SID_NAME = mrp816)
)
)

Tom Kyte

Followup  

February 04, 2003 - 12:25 pm UTC

well, the mrp in a database link has no connection, relationship or anything to mrp used in "sqlplus scott/tiger@mrp"

the mrp "host" in the dblink is resolved using the SERVERS tnsnames.ora -- not yours.

the mrp in the connect string scott/tiger@mrp is resolved using your tnsnames.ora.

the two most likely have nothing to do with eachother. You need to look at the tnsnames.ora file on the server, figure out what MRP means there and then you can determine why that server (which may will be different then your mrp server) is not responding.

Thank you

February 05, 2003 - 6:11 am UTC

Reviewer: Marcio from Brazil

ALWAYS -- You right.


Fake DB Links and connections

February 18, 2003 - 8:20 am UTC

Reviewer: C. Parmentier from France

Hi Tom,

I have a few more questions about DB Links, how will Oracle8i behaves when he sees a such SQL Request
(MYDB is NOT a DB Link, it's the name of the DB and no Loopback Links has been created for it)

SQLPLUS /@MYDB
SELECT * FROM MY_TABLE@MYDB

IMHO It runs like :
1) Read the database link tables to see if it is a dblink if so make a connection using that FALSE
2) Look at the order of the sqlnet.ora file to see where it is picking it's tnsname aliases from. In this case the format is TNSNAMES,ONAMES
3) Read tnsnames.ora to find out where MYDB is TRUE
4) Go out of the database and create a new oracle connection into the server and database - TRUE - resource used.

How can I really point this out using V$...

Thanks a lot for the help!

PS: You would say "Why ?, just remove the @MYDB of your request!" and you would be right ;) But, our process has to work on a single DB or on 3 DB for each areas...

PPS: You're really impossible to be reached at GMT+1 :) I should be working at night!

Tom Kyte

Followup  

February 18, 2003 - 9:13 am UTC

what is a "fake dblink"??


If your process has to work on a single db or 3 db's -- you should use VIEWS to hide that fact. You setup each database so the objects actually exist. Views can be used for location transparency very nicely.

No views

February 18, 2003 - 9:33 am UTC

Reviewer: C. Parmentier from France

Well, i'll keep the views in mind, would you please explain the case I proposed:

how does oracle behaves when Selecting from table@<localdbname>, will a new connection be created or will Oracle check that localdbname is not a Database Link and thus, won't look out the TNS and so on.

Thanks and Regards,


Tom Kyte

Followup  

February 18, 2003 - 6:43 pm UTC

<localdbname> WILL BE a database link. I don't know what you mean by "a fake database link".

March 02, 2003 - 11:17 pm UTC

Reviewer: green from China

Hi Tom,

I have database A,B,C.
I only have accounts for A and B, but in A I can use a public dblink to access the table in C, right now I want to access the table in C from the database B. Is it possible ?
Thanks!



Tom Kyte

Followup  

March 03, 2003 - 6:48 am UTC

if you create the same public dblink in B sure, else B will have to query a view on A that queries the table on C which would probably be about as slow as you could make it go.

March 03, 2003 - 11:57 am UTC

Reviewer: green from China

If I have not priviledges to create a view in A which is a Production database ( I only have SELECT priviledges)and no public link from B to C, so is it possible ?

Thanks!



Tom Kyte

Followup  

March 03, 2003 - 12:32 pm UTC

You'll need it -- or create synonym privilege.

there is no way to say "select * from (t@some_other_site)@some_site"

you would need a view or a synonym at some_site so you can query

select * from v@some_site
select * from s@some_site.



Global Name

March 04, 2003 - 7:08 am UTC

Reviewer: Abubaker Khered from Jeddah, Soudi Arabia

Hi Tom,

Is there any way to change global_name in DB 8.0.5., other then updating global_name table using sqlplus?


Thanks,
Abubaker

Tom Kyte

Followup  

March 04, 2003 - 6:11 pm UTC

umm, you cannot do that.

you can however use the ALTER DATABASE command.

March 04, 2003 - 12:48 pm UTC

Reviewer: jens

hello tom,

is there any way to set/get values of package variables on the remote database through a database link (our application uses such variables as an "environment" used within views).

Tom Kyte

Followup  

March 04, 2003 - 6:35 pm UTC

you need getter/setter routines. 

You MUST have "get" routines -- that is what the views would use as a view cannot just reference a PLSQL variable directly.

You should add "set" routines to set the values.

short of that, no not really:

ops$tkyte@ORA815> create synonym remote_pkg for remote_pkg@ora817dev.us.oracle.com;

Synonym created.

ops$tkyte@ORA815> exec remote_pkg.variable := 55;
BEGIN remote_pkg.variable := 55; END;

*
ERROR at line 1:
ORA-06550: line 1, column 18:
PLS-00512: Implementation Restriction: 'REMOTE_PKG.VARIABLE': Cannot directly access remote package variable or cursor
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored



(well, you could use DBMS_SQL@remote to dynamically execute a remote block but that would be painful) 

March 05, 2003 - 2:30 pm UTC

Reviewer: jens

is there any way to use packages variables on REMOTE site through set/get routines (package states are LOCAL to a session)?

Tom Kyte

Followup  

March 05, 2003 - 6:51 pm UTC

yes, if you have a package with getter/setter routines on the remote site, it works as normal (you HAVE a session on the remote site)

Loopback dblink

March 25, 2003 - 3:06 pm UTC

Reviewer: Dave from Prakash, India

Tom, could you please clarify what is a loopback db link and how it is useful? Thanks as always.

Tom Kyte

Followup  

March 25, 2003 - 8:32 pm UTC

it is what it sounds like, a dblink that connects back to the SAME database.

It is useful for testing...

It is useful for connecting as another user in your current session (eg: the loopback link can connect as scott/tiger whilst you are logged in as bob)...



example please

March 25, 2003 - 9:32 pm UTC

Reviewer: Dave

Tom, could you give an example? Thanks.

Tom Kyte

Followup  

March 26, 2003 - 7:21 am UTC

example of what?  a create database link statement??

ops$tkyte@ORA920> create database link ora920@loopback
  2  connect to scott
  3  identified by tiger
  4  using 'ora920';

Database link created.

ops$tkyte@ORA920> select * from dual@ora920@loopback;

D
-
X

ops$tkyte@ORA920> select * from emp;

no rows selected

ops$tkyte@ORA920> select count(*) from emp@ora920@loopback;

  COUNT(*)
----------
        14
 

Beautiful Information

March 26, 2003 - 3:48 am UTC

Reviewer: George Kennedy (GK) from USA

I've 4 databases A,B,C an D which are connected through one another through database links. A single schema can have multiple links which connect to different schemas on the remote database. All the links were created by using the option 'connect to <username> identified by <password>'. Now if I change the password of the user on database D which is referred by the links on A,B and C.

Can you please tell me
1. Do the links on A,B, and C become "INVALID" which access the particular schema in database D.
2. Do I've to re-create the DB links again on A,B, and C ? or is there any other way to recompile the links ?
3. How to identify the links which are affected on A,B and C by the password change ?

Tom Kyte

Followup  

March 26, 2003 - 7:43 am UTC

1) no, they just stop working.

2) yes, you need to recreate them.

3) select db_link, username from all_db_links;

Database Link and FGAC

March 28, 2003 - 1:37 pm UTC

Reviewer: Ray from Ottawa,On

I need to pull data from Server A to another server B periodically. Server A has data protected via FGAC and application context. What has to be done to access the data on server A?

tia for your help.

Tom Kyte

Followup  

March 28, 2003 - 4:12 pm UTC

just query it? FGAC is designed to be transparent

database links

April 23, 2003 - 11:35 am UTC

Reviewer: Rich from NJ

I was asked by my management to quantify the number of times a database link was used to connect to a remote database. Is there a way?

Thanks.

Tom Kyte

Followup  

April 23, 2003 - 7:30 pm UTC

easiest way I can think is you hide the links with views (lots of good reasons for doing that in any case) and audit selects on the views. That'll tell you pretty much "exactly"



database link and NTS

May 14, 2003 - 8:32 am UTC

Reviewer: Oracle-Leo from India

Hi,

I just faced a peculiar problem while using database links.
I have two databases on one Win2K server and wanted one DB to be accessed by another DB using database links. After creating the db link, when i tried to access the table in second DB using the command 'select * from url@abc', it gave me the error 'ORA-12640 Authentication adapter initialization failed'.

I found a note on web which stated that this could be resolved by commenting/removing the sqlnet.authenication_services='NTS' in SQLNET.ora file. It did solve my error, but was curious why did it matter. And how could I make it work with sqlnet.authentication_service=NTS.


Thanks

Tom Kyte

Followup  

May 14, 2003 - 3:13 pm UTC

you would need windows "security stuff" like domains and such such up. See the windows Oracle admin guide (part of your doc set). I run no windows, never set it up myself. It is security specific to that OS.

hide the link?????

May 14, 2003 - 5:58 pm UTC

Reviewer: Reader from Salt Lake City, UT

"easiest way I can think is you hide the links with views (lots of good reasons for doing that in any case) and audit selects on the views. That'll tell you
pretty much "exactly"".

Tom, what do you mean by hide the links with views? can you please clarify? I am going blank on this idea. any example would be appreciated. Thanks.


Tom Kyte

Followup  

May 14, 2003 - 11:39 pm UTC

create view v as select * from t@dblink;
grant select on v to ....;
audit the selects on v.


people don't use the dblink, they use a view.

performance implications?

May 14, 2003 - 9:52 pm UTC

Reviewer: Kamal Kishore from New Jersey, USA

Hi Tom,
Can't "count" how many times I have been benefited by the discussions and explanations here. Really learned a lot. This count query never returns - it's still counting - no matter how much we tune it...

As for the question:
In your earlier reply to this thread you said this:

"(and I'm not very fond of
public synonyms in GENERAL -- they have performance implications"


Just curious about the performance issues, if any, of using synonyms as compared to views? Apart from the maintenance issues and global confusion, Should we stay away from synonyms (to remote objects) and just use views? What performance issues should we be aware of?
Thanks,


Tom Kyte

Followup  

May 14, 2003 - 11:55 pm UTC

search for

steve adams public synonyms


on this site.

db links on other database platforms.

May 15, 2003 - 2:54 am UTC

Reviewer: Alvin from Philippines.

Are DB links Oracle only ?

can i create a dblink to another db platform say

oracle ->mySql
oracle ->sqlserver
oracle -> (new database platform)

do you have a link that some docs on 'DATABASE STANDARDS'.]

Thanks


Tom Kyte

Followup  

May 15, 2003 - 9:29 am UTC

a dblink is an oracle "device" if you will.

Others have similar things, but different. Many other databases cannot do distributed queries naturally -- they won't have dblinks or anything remotely similar.

Yes, you can create dblinks to other databases from Oracle - either via gateways (part of iAS) or via generic connectivity

</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:4406709207206 <code>




links

July 31, 2003 - 8:56 pm UTC

Reviewer: mo

Tom:

I copied a database to a laptop. I created two databases because it had links. When I exported tables from the second database PAP and treid to import it on the laptop it said it need DBA privileges so I imported them as system manager rather than PAPADMIN account.

I went to the first database INS and created a database link to PAP using system/manager since all tables are under that schema in the 2nd database.

When I tried to use it it gacve me an error:

ORA-12640: Authentication adapter initialization failed.

On another try with a different login I got

ORA-02019: Connection description from remore database not found. tnsnames.ora did have the service name.

Do you know what is causing these errors and what i have to do to fix it?

Thank you,

links

October 16, 2003 - 6:18 pm UTC

Reviewer: mo

Tom:

I have two servers A and B.  One server has oracle 8i and the other has 9i.  When I try to create a link I get an erros:

I execute this on server A (9i) in SQL*PLUS for windows.

SQL> create database link test
 connect to insadmin identified by insadmin
 using 'insd';

Database link created.

SQL> desc intreq@test;
ERROR:
ORA-12154: TNS:could not resolve service name

1.  Does this mean that service name 'insd' does not exist in the tnsnames.ora on the server.

2.  When you create a link that goes from one server to another is the definition in the tns entry where you key in the ip or the name of the other server.

Thanks 

Tom Kyte

Followup  

October 16, 2003 - 7:22 pm UTC

1) correct

2) the server the database you created the link is the one that needs to be able to resolve the link

ora-02019

November 17, 2003 - 9:30 pm UTC

Reviewer: dash

I created two DBLINK db1,db2.
(db1,db2 is right tnsname)

select * from test1@db1 is good.
select * from test2@db2 is good.
insert into test1@db1 values('..') is good.
insert into test2@db2 values('..') is good.

but
insert into test1@db1 (select * test2@db2) is error.

ORA-02019: connection description for remote database not found
ORA-02063: preceding stringstring from db(this db sid)
ORA-02063: 2 lines...(db1&#47196; ..)

how do I solve this problem?



Tom Kyte

Followup  

November 21, 2003 - 7:35 am UTC

let's see a sqlplus cut and paste of this.

Why display password?

November 19, 2003 - 2:03 am UTC

Reviewer: Praveen from India

Hi Tom,

I found out from all the three dblinks view that ALL_DB_LINKS and DBA_DB_LINKS doesn't display the password in literal text format. But USER_DB_LINKS displays the password as text. Why is it so and is there any workaround for hiding this password.

Thanks,
Praveen.

Tom Kyte

Followup  

November 21, 2003 - 11:24 am UTC

umm, you own the link -- you can only see your OWN private links. you already know the password.

November 21, 2003 - 4:50 pm UTC

Reviewer: Akhil from NJ

Hi Tom,

When the remote database password changes, how do we synch all the dblinks that use this password. We have different groups handling different instances which has dblinks pointing across each other. Our password policy requires frequent change of passwords for all database accounts. How can we automate this? Do you have any script / suggestions which will automatically synch the dblinks after the remote db password change? Thanks verymuch for your time.

Regards,
Akhil

Tom Kyte

Followup  

November 21, 2003 - 5:44 pm UTC

if you use GLOBAL USERS, then accounts are managed centrally - no need for passwords in each database.

if you use plain old user/passwords -- you are responsible for syncing them up. There is no way we can (we don't know what databases have a dblink that point to "us" -- we cannot sync them up)

Similar situation as dash above

December 04, 2003 - 9:18 am UTC

Reviewer: A reader from NJ

Hi Tom,

We had a similar situation where the inserts with a subquery over a DB link are not working. The individual SELECT queries are okay.

We had encountered it in the past, but dismissed it as something unusual since we were selecting on a table over DBLink1 which is actually a synonym for another table on DBLink2 as defined in DBLink1, and since it was new development, we just used other options available.

This time however, we encountered it on existing code after migrating our DEV environment from 8.1.7 to 9i.

Here's our environment information:

    Oracle9i Enterprise Edition Release 9.2.0.3.0 - 64bit Production
    PL/SQL Release 9.2.0.3.0 - Production
    CORE    9.2.0.3.0       Production
    TNS for Solaris: Version 9.2.0.3.0 - Production
    NLSRTL Version 9.2.0.3.0 - Production

We have created a workaround by prestoring the results of the subquery in a local table, but was wondering why we have had to do this. The problematic query was working in 8.1.7 before.

Thanks a lot for any insight you can provide on this matter. I have attached a copy of the log file for the sample SQLPlus session, with the INSERT statement in question added at the end.


    SQL>
    SQL> set timing on;
    SQL> set time on;
    08:40:08 SQL> set trimspool on;
    08:40:08 SQL>
    08:40:08 SQL> ------------------------------------------
    08:40:08 SQL> -- create test table
    08:40:08 SQL> ------------------------------------------
    08:40:08 SQL> drop table test_db_link;

    Table dropped.

    Elapsed: 00:00:00.01
    08:40:09 SQL>
    08:40:09 SQL> create table test_db_link
    08:40:09   2  as
    08:40:09   3  select tracknum, status, transdate, insseq
    08:40:09   4  from workhistory@wkl
    08:40:09   5  where rowid = '';

    Table created.

    Elapsed: 00:00:00.00
    08:40:09 SQL>
    08:40:09 SQL> desc test_db_link;
     Name                                      Null?    Type
     ----------------------------------------- -------- ----------------------------
     TRACKNUM                                  NOT NULL VARCHAR2(18)
     STATUS                                             CHAR(1)
     TRANSDATE                                          DATE
     INSSEQ                                             NUMBER

    08:40:09 SQL>
    08:40:09 SQL> select * from test_db_link;

    no rows selected

    Elapsed: 00:00:00.00
    08:40:09 SQL>
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> -- test subquery -- workhistory@wkl is indexed on insseq and tracknum
    08:40:09 SQL> --    with updated statistics
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> select distinct tracknum from workhistory@wkl where insseq = 142;

    TRACKNUM
    ------------------
    010600BAT51419PI

    Elapsed: 00:00:00.00
    08:40:09 SQL>
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> -- test select with subquery
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> select tracknum, status, transdate, insseq
    08:40:09   2  from workhistory@wkl
    08:40:09   3  where tracknum in (select distinct tracknum from workhistory@wkl where insseq = 142);

    TRACKNUM           S TRANSDATE     INSSEQ
    ------------------ - --------- ----------
    010600BAT51419PI   2 06-JAN-00        142
    010600BAT51419PI   2 07-JAN-00        143
    010600BAT51419PI   3 07-JAN-00        144
    010600BAT51419PI   5 07-JAN-00        145

    Elapsed: 00:00:00.00
    08:40:09 SQL>
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> -- test insert with select WITHOUT subquery
    08:40:09 SQL> ------------------------------------------
    08:40:09 SQL> insert into test_db_link
    08:40:09   2  select tracknum, status, transdate, insseq
    08:40:09   3  from workhistory@wkl
    08:40:09   4  where tracknum = '010600BAT51419PI'
    08:40:09   5  ;

    4 rows created.

    Elapsed: 00:00:00.00
    08:40:09 SQL>
    08:40:09 SQL> spool off;

    ------------------------------------------
    -- test insert with select WITH subquery
    --  WE HAD TO CANCEL THIS QUERY SINCE IT
    --  DOESN'T SEEM TO FINISH AT ALL, EVEN
    --  AFTER LEAVING IT RUNNING FOR SEVERAL
    --  MINUTES.
    ------------------------------------------
    insert into test_db_link
    select tracknum, status, transdate, insseq
    from workhistory@wkl
    where tracknum in (select distinct tracknum from workhistory@wkl where insseq = 142);


 

Tom Kyte

Followup  

December 04, 2003 - 9:51 am UTC

look at the query plans.

Here's the Explain Plan

December 04, 2003 - 10:34 am UTC

Reviewer: A reader from NJ

Hi Tom,

We decided to wait for the INSERT to finish. It took more than 15 minutes with the filter "insseq = 142". The actuak filter is "insseq >= :var".

Thanks a lot for your help. I will be sending in the TKPROF results as well.



SQL> 
SQL> set autotrace traceonly explain;
SQL> 
SQL> set timing on;
SQL> set time on;
10:08:57 SQL> set trimspool on;
10:08:57 SQL> ----------------------------------------------------------------------
10:09:03 SQL> -- test subquery
10:09:03 SQL> ----------------------------------------------------------------------
10:09:03 SQL> select distinct tracknum from workhistory@wkl where insseq = 142;
Elapsed: 00:00:00.00

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT (REMOTE) Optimizer=CHOOSE (Cost=4 Card=1 By
          tes=21)

   1    0   TABLE ACCESS (BY INDEX ROWID) OF 'WORKHISTORY' (Cost=2 Car ORANETRA
          d=1 Bytes=21)

   2    1     INDEX (UNIQUE SCAN) OF 'WKLHINSSEQ' (UNIQUE) (Cost=2 Car ORANETRA
          d=1140186)




10:09:03 SQL> 
10:09:03 SQL> ----------------------------------------------------------------------
10:09:14 SQL> -- test select with subquery
10:09:14 SQL> ----------------------------------------------------------------------
10:09:14 SQL> select tracknum, status, transdate, insseq
10:09:14   2  from workhistory@wkl
10:09:14   3  where tracknum in (select distinct tracknum from workhistory@wkl where insseq = 142);
Elapsed: 00:00:00.00

Execution Plan
----------------------------------------------------------
   0      SELECT STATEMENT (REMOTE) Optimizer=CHOOSE (Cost=4 Card=1 By
          tes=50)

   1    0   NESTED LOOPS (Cost=4 Card=1 Bytes=50)
   2    1     TABLE ACCESS (BY INDEX ROWID) OF 'WORKHISTORY' (Cost=2 C ORANETRA
          ard=1 Bytes=21)

   3    2       INDEX (UNIQUE SCAN) OF 'WKLHINSSEQ' (UNIQUE) (Cost=2 C ORANETRA
          ard=1140186)

   4    1     TABLE ACCESS (BY INDEX ROWID) OF 'WORKHISTORY' (Cost=2 C ORANETRA
          ard=1 Bytes=29)

   5    4       INDEX (RANGE SCAN) OF 'WKHTRACKNUMIDX' (NON-UNIQUE)    ORANETRA



10:09:14 SQL> 
10:09:14 SQL> ----------------------------------------------------------------------
10:09:14 SQL> -- test insert with select WITHOUT subquery
10:09:14 SQL> ----------------------------------------------------------------------
10:09:14 SQL> insert into test_db_link
10:09:14   2  select tracknum, status, transdate, insseq
10:09:14   3  from workhistory@wkl
10:09:14   4  where tracknum = '010600BAT51419PI'
10:09:14   5  ;

4 rows created.

Elapsed: 00:00:00.00

Execution Plan
----------------------------------------------------------
   0      INSERT STATEMENT Optimizer=CHOOSE (Cost=4 Card=1 Bytes=36)
   1    0   REMOTE* (Cost=4 Card=1 Bytes=36)                           WKL


   1 SERIAL_FROM_REMOTE            SELECT "TRACKNUM","STATUS","TRANSDATE","INSS
                                   EQ" FROM "WORKHISTORY" "WORKHISTORY"


10:09:14 SQL> 
10:09:15 SQL> ----------------------------------------------------------------------
10:09:24 SQL> -- test insert with select WITH subquery
10:09:24 SQL> ----------------------------------------------------------------------
10:09:24 SQL> insert into test_db_link
10:09:24   2  select tracknum, status, transdate, insseq
10:09:24   3  from workhistory@wkl
10:09:24   4  where tracknum in (select distinct tracknum from workhistory@wkl where insseq = 142);

4 rows created.

Elapsed: 00:15:36.00

Execution Plan
----------------------------------------------------------
   0      INSERT STATEMENT Optimizer=CHOOSE (Cost=172346 Card=57009 By
          tes=2052324)

   1    0   FILTER
   2    1     REMOTE* (Cost=1319 Card=57009 Bytes=2052324)             WKL
   3    1     REMOTE* (Cost=3 Card=1 Bytes=24)                         WKL


   2 SERIAL_FROM_REMOTE            SELECT "TRACKNUM","STATUS","TRANSDATE","INSS
                                   EQ" FROM "WORKHISTORY" "SYS_ALIAS_1"

   3 SERIAL_FROM_REMOTE            SELECT "TRACKNUM","INSSEQ" FROM "WORKHISTORY
                                   " "WORKHISTORY" WHERE "TRACKNUM"=:1


10:25:00 SQL> 
10:25:00 SQL> spool off;
 

Tom Kyte

Followup  

December 04, 2003 - 11:09 am UTC

so it is pulling both back and then processing.


if you use driving_site and push to the remote does it affect the plan (just use autotrace traceonly explain, no need to run it)

And here's the TKProf output

December 04, 2003 - 10:35 am UTC

Reviewer: A reader from NJ

Hi Tom,

Here's what we got from TKPROF.

Thanks.


TKPROF: Release 9.2.0.3.0 - Production on Thu Dec 4 10:21:54 2003

Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.

Trace file: metrics_ora_12441_TESTDBLINK.trc
Sort options: default

********************************************************************************
count = number of times OCI procedure was executed
cpu = cpu time in seconds executing
elapsed = elapsed time in seconds executing
disk = number of physical reads of buffers from disk
query = number of buffers gotten for consistent read
current = number of buffers gotten in current mode (usually for update)
rows = number of rows processed by the fetch or execute call
********************************************************************************

alter session set events '10046 trace name context forever, level 8'


call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 0 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 1 0.00 0.00 0 0 0 0

Misses in library cache during parse: 0
Optimizer goal: CHOOSE
Parsing user id: 43

Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.02 0.02
SQL*Net message to dblink 11 0.00 0.00
SQL*Net message from dblink 11 0.02 0.05
********************************************************************************

insert into test_db_link
select tracknum, status, transdate, insseq
from workhistory@wkl
where tracknum in (select distinct tracknum from workhistory@wkl where insseq = 142)

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.03 0.15 0 4 1 0
Execute 1 617.98 1083.94 0 1 3 4
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 618.01 1084.10 0 5 4 4

Misses in library cache during parse: 0
Optimizer goal: CHOOSE
Parsing user id: 43

Rows Row Source Operation
------- ---------------------------------------------------
4 FILTER (cr=0 r=0 w=0 time=2977732 us)
1139808 REMOTE (cr=0 r=0 w=0 time=90516637 us)
1 REMOTE (cr=0 r=0 w=0 time=62446423 us)


Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to dblink 868838 0.00 3.02
SQL*Net message from dblink 868838 0.64 641.27
SQL*Net more data from dblink 16095 0.02 2.57
latch free 1 0.00 0.00
SQL*Net message to client 1 0.00 0.00
SQL*Net message from client 1 0.05 0.05
********************************************************************************

alter session set events '10046 trace name context off'


call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 2 0.00 0.00 0 0 0 0

Misses in library cache during parse: 0
Optimizer goal: CHOOSE
Parsing user id: 43



********************************************************************************

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 2 0.03 0.15 0 4 1 0
Execute 3 617.98 1083.94 0 1 3 4
Fetch 0 0.00 0.00 0 0 0 0
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 5 618.01 1084.10 0 5 4 4

Misses in library cache during parse: 0

Elapsed times include waiting on following events:
Event waited on Times Max. Wait Total Waited
---------------------------------------- Waited ---------- ------------
SQL*Net message to client 2 0.00 0.00
SQL*Net message from client 2 0.05 0.07
SQL*Net message to dblink 868849 0.00 3.02
SQL*Net message from dblink 868849 0.64 641.32
SQL*Net more data from dblink 16095 0.02 2.57
latch free 1 0.00 0.00


OVERALL TOTALS FOR ALL RECURSIVE STATEMENTS

call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.01 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 4 0 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.01 0.00 0 4 0 1

Misses in library cache during parse: 0

3 user SQL statements in session.
1 internal SQL statements in session.
4 SQL statements in session.
********************************************************************************
Trace file: metrics_ora_12441_TESTDBLINK.trc
Trace file compatibility: 9.00.01
Sort options: default

1 session in tracefile.
3 user SQL statements in trace file.
1 internal SQL statements in trace file.
4 SQL statements in trace file.
4 unique SQL statements in trace file.
1753850 lines in trace file.




Re-written Query

December 04, 2003 - 12:05 pm UTC

Reviewer: A reader from NJ

Hi Tom,

We are not quite sure how to "use driving_site and push to the remote".

That did prod us to rethink our query, though, and we just combined the subquery with the other one, eliminating both the temporary table and the subquery. We just re-wrote the query to use SELECT DISTINCT and joins over the DBLink.

While we still don't quite understand what was wrong with the INSERT over a DBLINK using a SELECT with a SUBQUERY, we are quite satisfied with the new workaround. We just hope that we don't encounter this problem again later, as this is the second time that we did.

Thanks again.

11:52:51 SQL> 
11:52:51 SQL> set autotrace traceonly explain;
11:52:51 SQL> 
11:52:51 SQL> set timing on;
11:52:51 SQL> set time on;
11:52:51 SQL> set trimspool on;
11:52:51 SQL> 
11:52:51 SQL> ----------------------------------------------------------------------
11:52:51 SQL> -- test insert with JOINS on DB LINKS (exact INSSEQ)
11:52:51 SQL> ----------------------------------------------------------------------
11:52:51 SQL> insert into test_db_link
11:52:51   2  select  DISTINCT a.tracknum, a.status, a.transdate, a.insseq
11:52:51   3  from    workhistory@wkl a, workhistory@wkl b
11:52:51   4  where   a.tracknum = b.tracknum
11:52:51   5  and     b.insseq=142
11:52:51   6  ;

4 rows created.

Elapsed: 00:00:00.00

Execution Plan
----------------------------------------------------------
   0      INSERT STATEMENT Optimizer=CHOOSE (Cost=12 Card=1 Bytes=60)
   1    0   SORT (UNIQUE) (Cost=12 Card=1 Bytes=60)
   2    1     NESTED LOOPS (Cost=8 Card=1 Bytes=60)
   3    2       REMOTE* (Cost=3 Card=1 Bytes=24)                       WKL
   4    2       REMOTE*                                                WKL


   3 SERIAL_FROM_REMOTE            SELECT "TRACKNUM","INSSEQ" FROM "WORKHISTORY
                                   " "B" WHERE "INSSEQ"=142

   4 SERIAL_FROM_REMOTE            SELECT "TRACKNUM","STATUS","TRANSDATE","INSS
                                   EQ" FROM "WORKHISTORY" "A" WHERE "TR


11:52:51 SQL> 
11:52:51 SQL> ----------------------------------------------------------------------
11:52:51 SQL> -- test insert with JOINS on DB LINKS (from last INSSEQ)
11:52:51 SQL> ----------------------------------------------------------------------
11:52:51 SQL> insert into test_db_link
11:52:51   2  select  DISTINCT a.tracknum, a.status, a.transdate, a.insseq
11:52:51   3  from    workhistory@wkl a, workhistory@wkl b
11:52:51   4  where   a.tracknum = b.tracknum
11:52:51   5  and     b.insseq >= 14500000
11:52:51   6  ;

29861 rows created.

Elapsed: 00:00:11.05

Execution Plan
----------------------------------------------------------
   0      INSERT STATEMENT Optimizer=CHOOSE (Cost=1402 Card=1139 Bytes
          =68340)

   1    0   SORT (UNIQUE) (Cost=1402 Card=1139 Bytes=68340)
   2    1     REMOTE* (Cost=1319 Card=1140186 Bytes=41046696)          WKL


   2 SERIAL_FROM_REMOTE            SELECT "A1"."TRACKNUM","A1"."STATUS","A1"."T
                                   RANSDATE","A1"."INSSEQ","A1"."TRACKN


11:53:03 SQL> 
11:53:03 SQL> spool off;
 

December 11, 2003 - 10:36 am UTC

Reviewer: Kashif from Reston, VA

Hi Tom,

You mentioned in one of your responses:

"so it is pulling both back and then processing."

which I understood to mean that instead of executing the query remotely and bringing down the result data, the statement brought the data down to the local db and then did the work. Is that correct?

Secondly, how were you able to tell that that is what happened?

Finally, what does the term "SERIAL_FROM_REMOTE" in the Execution Plan mean? I looked the term up in the Performance Tuning Guide, and here's what it said: 'Serial execution at a remote site'. Which I understand to mean that the query was executed remotely, and then the results brought down to the local db. But that does not sound like what you had concluded for that query.

Any feedback would be helpful. Thanks.

Kashif

Tom Kyte

Followup  

December 11, 2003 - 12:21 pm UTC

the query plan showed us that -- two remote operations followed by a filter. gives us the remote query that was executed and all.

it is basically taking:

2 select tracknum, status, transdate, insseq
10:09:24 3 from workhistory@wkl
10:09:24 4 where tracknum in (select distinct tracknum from workhistory@wkl
where insseq = 142);

and executing it like this:


for x in ( select * from remote_table )
loop
query remote table again by tracknum to get tracknum and insseq

if one of the the returned insseq's is 142
then
output record
end if
end loop

Execution Plan
----------------------------------------------------------
0 INSERT STATEMENT Optimizer=CHOOSE (Cost=172346 Card=57009 By
tes=2052324)

1 0 FILTER
2 1 REMOTE* (Cost=1319 Card=57009 Bytes=2052324) WKL
3 1 REMOTE* (Cost=3 Card=1 Bytes=24) WKL


2 SERIAL_FROM_REMOTE SELECT "TRACKNUM","STATUS","TRANSDATE","INSS
EQ" FROM "WORKHISTORY" "SYS_ALIAS_1"

3 SERIAL_FROM_REMOTE SELECT "TRACKNUM","INSSEQ" FROM "WORKHISTORY
" "WORKHISTORY" WHERE "TRACKNUM"=:1

confusing on the db links

January 07, 2004 - 10:18 pm UTC

Reviewer: mike


Tom,
I have a database DB_X on server X. I want to create the database links to two remote databases DB_Y1/Y2 on two
different server Y1/Y2.
The tnsnames.ora:

DB_Y1 = (DESCRIPTION=
(ADDRESS=(PROTOCOL=tcp)(HOST=serv_y1)(PORT=1526))
(CONNECT_DATA=(SID=DB_Y1))
)
DB_Y2 = (DESCRIPTION=
(ADDRESS=(PROTOCOL=tcp)(HOST=serv_y2)(PORT=1531))
(CONNECT_DATA=(SID=DB_Y2))
)

To create the database links, for DBY1 the following works:
create database link DBY1 connect to user1 identified by user1 using 'DB_Y1'
/

However the db link for DBY2 does not work if the format of creation used as above.

I have to create it as :
create database link DBY2 connect to user1 identified by user1
using '(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=serv_y2)(PORT=1531))(CONNECT_DATA=(SID=DB_Y2)))'
/

Question: for what reasons the full description of tnsname has to be used for the DB_Y2/serv_y2?

Tom Kyte

Followup  

January 08, 2004 - 12:42 pm UTC

are you showing me the tnsnames.ora entry FROM THE DATABASE SERVER

or are you showing me YOUR tnsnames.ora entry, and the one on the server only really has db_y1 in it.

the dblink cannot see "your" tnsnames.ora, it sees the one on the database server.

sorry for was not very clear

January 08, 2004 - 1:58 pm UTC

Reviewer: A reader

The tnsnames.ora entry shown is on server X. DB_X is on server X.
Both DB_Y1 and DB_Y2 are on remote servers (two different servers or machines).
The db link in question is on DB_X to DB_Y2 on server Y2


Mike

Tom Kyte

Followup  

January 08, 2004 - 3:33 pm UTC

i don't see the "error" but tell you what. log DIRECTLY INTO the server with DB_X

show us a CUT AND PASTE of

$ tnsping db_y1
$ tnsping db_y2
$ sqlplus u/p
create database link to y1
select * from dual@y1
create database link to y2
select * from dual@y2


CUT AND PASTE it, no editing

synonym for remote stored function doesn't work

February 05, 2004 - 5:40 pm UTC

Reviewer: James Su from Toronto CA

SQL> create or replace function ff return number is begin return 200; end;
  2  /

Function created.

SQL> conn XXXX/XXXX@dev32
Connected.


SQL> create database link dbl_rep connect to XXXXXXX identified by XXXXXXXX using 'dev2';

Database link created.

SQL> select * from dual@dbl_rep;

D
-
X

SQL> select ff@dbl_rep from dual;

        FF
----------
       200

SQL> create or replace synonym sy_test for ff@dbl_rep;

Synonym created.

SQL> select sy_test from dual;
select sy_test from dual
       *
ERROR at line 1:
ORA-00904: "SY_TEST": invalid identifier
 

Tom Kyte

Followup  

February 06, 2004 - 8:30 am UTC

should work fine:

ops$tkyte@ORA9IR2> create or replace function ff return number
  2  as
  3  begin
  4  return 55;
  5  end;
  6  /
 
Function created.
 
ops$tkyte@ORA9IR2> select ff@ora9ir2@loopback from dual;
 
        FF
----------
        55
 
ops$tkyte@ORA9IR2> create or replace synonym sy_test for ff@ora9ir2@loopback;
 
Synonym created.
 
ops$tkyte@ORA9IR2> select sy_test from dual;
 
   SY_TEST
----------
        55
 
ops$tkyte@ORA9IR2>


Please contact support for this one. 

Incorrect Results on DB Link Query

April 01, 2004 - 12:12 pm UTC

Reviewer: A reader from NJ

Hi Tom,

I was wondering whether you could explain this behavior to us. We already have a correct, working query, but took us quite sometime figuring out what was wrong with the initial query in the first place. We know we should always compare strings to strings, numbers to numbers, but we were wondering why the first query below was not returning any results, whereas a similar query with more filters was returning some, but incorrect results:

-----------------------------------
-- w/base filter
-----------------------------------
    -----------------------------------
    --  Inner query produces MORE results
    -----------------------------------
    11:54:49 SQL>
    11:54:49 SQL> /* Formatted on 2004/04/01 11:01 (Formatter Plus v4.8.0) */
    11:54:49 SQL> SELECT  ftsroamid
    11:54:49   2  FROM    getstatus
    11:54:49   3  WHERE   ordernum LIKE 'FTSSV20040401%'
    11:54:49   4  ;

    FTSROAMID
    ----------------
    2004040100321000
    2004040100321000
    2004040100321000
    2004040100322000
    2004040100323000
    2004040100324000
    2004040100324000
    2004040100325000
    2004040100326000
    2004040100327000
    2004040100328000
    2004040100329000
    2004040100330000
    2004040100331000
    2004040100332000
    2004040100333000
    2004040100334000
    2004040100335000
    2004040100336000
    2004040100337000
    2004040100338000
    2004040100339000
    2004040100340000
    2004040100341000
    2004040100342000
    2004040100343000
    2004040100344000
    2004040100345000
    2004040100346000

    29 rows selected.

    Elapsed: 00:00:00.00

    -----------------------------------
    -- but final query DOES NOT RETURN ANY!
    -----------------------------------
    11:54:49 SQL>
    11:54:49 SQL> SELECT  TO_CHAR (time_key_stamp, '0000000000000000') time_key_stamp
    11:54:49   2  FROM    fts_address_info@lk_roamprod
    11:54:49   3  WHERE   time_key_stamp IN
    11:54:49   4          (
    11:54:49   5          SELECT ftsroamid
    11:54:49   6          FROM   getstatus
    11:54:49   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:49   8          )
    11:54:49   9  ;

    no rows selected

    Elapsed: 00:00:03.02

-----------------------------------
-- w/additional filter
-----------------------------------
    -----------------------------------
    -- Inner query produces LESS results
    -----------------------------------
    11:54:52 SQL>
    11:54:52 SQL> SELECT  ftsroamid
    11:54:52   2  FROM    getstatus
    11:54:52   3  WHERE   ordernum LIKE 'FTSSV20040401%'
    11:54:52   4  AND     getstatus = 'R'
    11:54:52   5  ;

    FTSROAMID
    ----------------
    2004040100321000
    2004040100321000
    2004040100321000
    2004040100322000
    2004040100323000
    2004040100324000
    2004040100324000

    7 rows selected.

    Elapsed: 00:00:00.00

    -----------------------------------
    -- but final query RETURNS SOME, BUT THE RESULTS ARE INCORRECT!
    -----------------------------------
    11:54:52 SQL>
    11:54:52 SQL> SELECT  TO_CHAR (time_key_stamp, '0000000000000000') time_key_stamp
    11:54:52   2  FROM    fts_address_info@lk_roamprod
    11:54:52   3  WHERE   time_key_stamp IN
    11:54:52   4          (
    11:54:52   5          SELECT ftsroamid
    11:54:52   6          FROM   getstatus
    11:54:52   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:52   8          AND     getstatus = 'R'
    11:54:52   9          )
    11:54:52  10  ;

    TIME_KEY_STAMP
    ----------------
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000

    8 rows selected.

    Elapsed: 00:00:01.03


    -----------------------------------
    -- FINAL QUERY WITH EXPECTED RESULTS:
    -----------------------------------
    11:54:54 SQL>
    11:54:54 SQL>
    11:54:54 SQL> SELECT  TRIM (TO_CHAR (time_key_stamp, '0000000000000000')) time_key_stamp
    11:54:54   2  FROM    fts_address_info@lk_roamprod
    11:54:54   3  WHERE   TRIM (TO_CHAR (time_key_stamp, '0000000000000000')) IN
    11:54:54   4          (
    11:54:54   5          SELECT ftsroamid
    11:54:54   6          FROM   getstatus
    11:54:54   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:54   8          )
    11:54:54   9  ;

    TIME_KEY_STAMP
    ----------------
    2004040100321000
    2004040100321000
    2004040100322000
    2004040100322000
    2004040100323000
    2004040100323000
    2004040100324000
    2004040100324000

    8 rows selected.

    Elapsed: 00:00:00.05

    -----------------------------------
    -- we also tried TO_NUMBER/NVL on the inner query, but still failed.
    -----------------------------------
    11:54:54 SQL>
    11:54:54 SQL> SELECT  time_key_stamp
    11:54:54   2  FROM    fts_address_info@lk_roamprod
    11:54:54   3  WHERE   time_key_stamp IN
    11:54:54   4          (
    11:54:54   5          SELECT TO_NUMBER(NVL(ftsroamid,0))
    11:54:54   6          FROM   getstatus
    11:54:54   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:54   8          )
    11:54:54   9  ;

    no rows selected

    Elapsed: 00:00:06.00

    -----------------------------------
    -- as well as TO_NUMBER/IS NOT NULL on the inner query, and still failed.
    -----------------------------------
    11:55:00 SQL>
    11:55:00 SQL> SELECT  time_key_stamp
    11:55:00   2  FROM    fts_address_info@lk_roamprod
    11:55:00   3  WHERE   time_key_stamp IN
    11:55:00   4          (
    11:55:00   5          SELECT TO_NUMBER(ftsroamid)
    11:55:00   6          FROM   getstatus
    11:55:00   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:55:00   8          AND    ftsroamid IS NOT NULL
    11:55:00   9          )
    11:55:00  10  ;

    no rows selected


Here's our environment information:

    LOCAL
        Oracle9i Enterprise Edition Release 9.2.0.3.0 - 64bit Production
        PL/SQL Release 9.2.0.3.0 - Production
        CORE    9.2.0.3.0   Production
        TNS for Solaris: Version 9.2.0.3.0 - Production
        NLSRTL Version 9.2.0.3.0 - Production

    REMOTE
        Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
        PL/SQL Release 9.2.0.1.0 - Production
        CORE    9.2.0.1.0   Production
        TNS for Solaris: Version 9.2.0.1.0 - Production
        NLSRTL Version 9.2.0.1.0 - Production

Thanks a lot in advance.
 

Tom Kyte

Followup  

April 01, 2004 - 1:02 pm UTC

this indicates "bug" - please contact support:

  11:54:49 SQL> SELECT  TO_CHAR (time_key_stamp, '0000000000000000') 
time_key_stamp
    11:54:49   2  FROM    fts_address_info@lk_roamprod
    11:54:49   3  WHERE   time_key_stamp IN
    11:54:49   4          (
    11:54:49   5          SELECT ftsroamid
    11:54:49   6          FROM   getstatus
    11:54:49   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:49   8          )
    11:54:49   9  ;

    no rows selected

    11:54:52 SQL>
    11:54:52 SQL> SELECT  TO_CHAR (time_key_stamp, '0000000000000000') 
time_key_stamp
    11:54:52   2  FROM    fts_address_info@lk_roamprod
    11:54:52   3  WHERE   time_key_stamp IN
    11:54:52   4          (
    11:54:52   5          SELECT ftsroamid
    11:54:52   6          FROM   getstatus
    11:54:52   7          WHERE  ordernum LIKE 'FTSSV20040401%'
    11:54:52   8          AND     getstatus = 'R'
    11:54:52   9          )
    11:54:52  10  ;

    TIME_KEY_STAMP
    ----------------
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000
     2004040100324000

    8 rows selected. 

dead process caused by dblink

April 13, 2004 - 12:41 pm UTC

Reviewer: John from Canada

Hi Tom,

I have PL/SQL procedure which copies data from remote database. Both databases are 9.0.1. Most of time the procedure is running fine. However, when the remote database has some unexpected problem (like shutdown, etc... but not all the shutdown cause the problem) it cause the procedure hang and do nothing. My procedure looks like below:
Loop
begin
insert into table as select * from table@remote;
sleep 20 seconds;
exception
when others then
record error...
end;
end loop;
Since we cannot control the remote database, we cannot use materialize view with fast refresh. This is the only approach we can make.

If the process is hang, we can only kill the process and re-start it. Even for killing the process, the process was marked as killed, not totally killed right away.

The exception statement in the above code does catch some errors but not catch this kind of errors.Is there any way to let the procedure detect the problem by itself and avoid the killing?

Many thanks.

Tom Kyte

Followup  

April 13, 2004 - 6:25 pm UTC

well, most likely this is your tcp-ip settings at the OS level. TCP-IP isn't timing out the dead connection on the other end -- you'll wait till they do.

Talk to your system admins and see what they can do to help you out....

(why sleep for 20 seconds??)

April 14, 2004 - 12:49 pm UTC

Reviewer: John from Canada

Hi Tom,

Thanks for your answer.

Do you mean TCP/IP on remote server should timeout the dead connection? How does the TCP/IP know whether the oracle connection is dead? Is there any reference link in Oracle Doc? Since I recorded errors, I did see some messages:
ORA-03113: end-of-file on communication channel
ORA-12535: TNS:operation timed out
Are these messages caused by TCP/IP?

The reason for sleeping 20 seconds is we want almost real-time data, quick response for the query on our side and less effect on the remote side.

Thanks.


Tom Kyte

Followup  

April 14, 2004 - 2:09 pm UTC

tcp/ip on the local machine (the machine that is still alive) is what needs to time out.

that error message is caused by tcp/ip finally timing out the connection -- yes.

How can I access a Procedure throw a database link?

May 05, 2004 - 1:55 pm UTC

Reviewer: Ricardo Patrocinio from Porto, Portugal

I tried exec my$procedure@mydblink;

But it didn't work!?


Thank you

Tom Kyte

Followup  

May 05, 2004 - 3:10 pm UTC

my car won't start either!?

ops$tkyte@ORA9IR2> exec my$procedure@ora9i;
 
PL/SQL procedure successfully completed.


care to share the error. 

Time out error

June 02, 2004 - 10:09 am UTC

Reviewer: Anil Pant

Hi,
As per your previous response to one of the query regarding the TNS:operation timed out, you said it always takes SERVER tnsnames.ora

I referred to SERVER tnsnames.ora.
Service_Name in SERVER tnsnames.ora is same as name used in USING 'srini' of CREATE Database Link

The SERVER tnsnames.ora is

SRINI =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.4.12.108)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = srini)
)
)

I created a database link

create database link tosrini2
connect to xyz
identified by xyz
using 'srini';

But when I give the select statement,
select * from cbbsp_payee@tosrini2;

I get the error,
ERROR at line 1:
ORA-12535: TNS:operation timed out

What could be the error ?

select * from cbbsp_payee@srini;



Tom Kyte

Followup  

June 02, 2004 - 11:20 am UTC

> oerr ora 12535
12535, 00000, "TNS:operation timed out"
// *Cause: The requested connection could not be completed within the timeout
// period specified by the CONNECT_TIMEOUT parameter in listener.ora. This
// error arises from the tnslsnr.
// *Action: Either reconfigure CONNECT_TIMEOUT to be 0, which means
// wait indefinitely, or reconfigure CONNECT_TIMEOUT to be some higher
// value. Or, if the timeout is unacceptably long, turn on tracing
// for further information.



Time out error ...Forgot to mention the version

June 02, 2004 - 10:14 am UTC

Reviewer: Anil Pant

Forgot to mention the version. Im using Oracle 9.2 on NT.

Hi,
As per your previous response to one of the query regarding the TNS:operation
timed out, you said it always takes SERVER tnsnames.ora

I referred to SERVER tnsnames.ora.
Service_Name in SERVER tnsnames.ora is same as name used in USING 'srini' of
CREATE Database Link

The SERVER tnsnames.ora is

SRINI =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 10.4.12.108)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = srini)
)
)

I created a database link

create database link tosrini2
connect to xyz
identified by xyz
using 'srini';

But when I give the select statement,
select * from cbbsp_payee@tosrini2;

I get the error,
ERROR at line 1:
ORA-12535: TNS:operation timed out

What could be the error ?

select * from cbbsp_payee@srini;


Database Link

July 05, 2004 - 2:12 pm UTC

Reviewer: A reader

Hi Tom

I am using database links to pull data from production database into a reporting datamart. I am being told that it is not a good practice to use database links to import data. The explanation is - Ideally the source system should have control and make data available to other systems in form of files. Is this right? I have worked on systems which would create snapshots using dblinks. Could you please highlight the disadvantages of using dblinks.

Thanks

Tom Kyte

Followup  

July 05, 2004 - 2:23 pm UTC

Another way to put this is

"the source system should not recognize the investment in software that this company has made. The source system should have programers just sitting around writing code to specification for anyone that needs data from us. The source system should use technology the from 1960's (flat files, sneaker net) in order to exchange information. The source system should lose all capabilities to audit and secure information. the source system should be a thorn in the side of everyone."

or put shorter

"no, i disagree totally".

Maybe dblinks are not always the correct answer but to say "dump and load to files is the only way" is somewhat short sighted.



Database links

July 06, 2004 - 4:31 am UTC

Reviewer: A reader

Wonderful explanation, Thanks very much.

Dblink and Performance

July 07, 2004 - 2:19 am UTC

Reviewer: Arul from India

Hello Sir,


-- I have two databases X and Y. X has empx table and Y has empy table.
-- Want to query empx(with million records) and insert selected (may be few rows) data into empy table using dblink.

-- Which one is best out of below 2 from performance prospective and Why ?

1. From database X

insert into empy@Y select * from empx where...

OR

2. From database Y

insert into empy select * from empx@X where...


-- What will happen in above case internally ?

In case 1..

-- Will it select all million rows of empx and carry to database Y and filter there and then insert few selected rows in empy table or else it will select and filter rows here in database X and only carry few rows for insertion to empy table of Y database ?

-- How to figure out that from explain plan ?

Thanx in Advance...


Tom Kyte

Followup  

July 07, 2004 - 8:07 am UTC

I'd probably want to do #1.

the query is in need of the most optimization here, database X is best suited to perform the optimization.


explain plan shows you the explain plan for distributed as well as single site queries.

Example please

July 08, 2004 - 12:19 am UTC

Reviewer: Arul from India

Hello Sir,

-- I would really appreciate if you brief answer for #2 with an example.

Thanxn in Advance.

Tom Kyte

Followup  

July 08, 2004 - 8:14 am UTC

you already gave the example for #2? not sure what else you would want there.

you would use explain plan to see "what would happen"

Check the validity of db links..?

July 12, 2004 - 3:36 am UTC

Reviewer: Naveen C from Bangalore

How do we check the validity for all the db-links the database..? Is there any automated process..?

Tom Kyte

Followup  

July 12, 2004 - 11:20 am UTC

define "validity", what if a server is just down for a moment.

they are all "valid", they might not be pointing to a server that exists -- but hopefully you would know that? so, just query dba_db_links and look at the tns connect strings and verify they "ok"

dba_db_links

July 12, 2004 - 9:19 pm UTC

Reviewer: Naveen C from Bangalore

Thanks.. very much..

Insertion via dblinks fails

July 13, 2004 - 8:41 am UTC

Reviewer: Arul from India

Hello Sir,

I have very strange problem as described below.

Below statement runs fine.

SELECT SBCNO ,
SCURRENTBCNO ,
SGENERATIONCODE ,
SHEADBCNO ,
CACTIONFLAG ,
SGROUPID ,
to_date('20040712','yyyymmdd')
FROM test_table A
WHERE SBCNO IN (SELECT D.BATCHCARD_NO
FROM SCORDERD D,
SORDERM M
WHERE M.SO_NO=D.SO_NO
AND M.STATUS='CLOSE'
AND D.BATCHCARD_NO='T3027715.11'
AND M.CLOSE_DATE<=SYSDATE-174)

Optimizer goal: RULE


Rows Execution Plan
------- ---------------------------------------------------
0 SELECT STATEMENT GOAL: RULE
0 NESTED LOOPS
1 VIEW
1 SORT (UNIQUE)
1 NESTED LOOPS
1 TABLE ACCESS (BY ROWID) OF 'SCORDERD'
2 INDEX GOAL: ANALYZED (RANGE SCAN) OF
'SCORDERD_N2' (NON-UNIQUE)
1 TABLE ACCESS (BY ROWID) OF 'SORDERM'
2 INDEX GOAL: ANALYZED (RANGE SCAN) OF
'SORDERM_N1' (NON-UNIQUE)
0 TABLE ACCESS (BY ROWID) OF 'test_table'
1 INDEX (RANGE SCAN) OF 'test_table_N01' (NON-UNIQUE)

But below statement fails with ORA-01652

INSERT INTO test_table@CELL3
SELECT SBCNO ,
SCURRENTBCNO ,
SGENERATIONCODE ,
CACTIONFLAG ,
SGROUPID ,
to_date('20040712','yyyymmdd')
FROM test_table A
WHERE SBCNO IN (SELECT D.BATCHCARD_NO
FROM SORDERM D,
SCORDERD M
WHERE M.SO_NO=D.SO_NO
AND M.STATUS='CLOSE'
AND D.BATCHCARD_NO='T3027715.11'
AND M.CLOSE_DATE<=SYSDATE-174)


Optimizer goal: RULE

Rows Execution Plan
------- ---------------------------------------------------
0 INSERT STATEMENT GOAL: RULE (REMOTE)
0 MERGE JOIN
0 SORT (JOIN)
0 REMOTE [!]
SELECT "SBCNO","SCURRENTBCNO","SGENERATIONCODE","SHEADBCNO",
"SSTAGE","LMAINQTY","SPROG","STESTTIME","STESTTIMEUNIT",
"STEMP","CHEAD","SMOID","FMAINQTY","SEQPID","SHP_QTY",
"INODE","IHEADNODE","SPARENTBCNO","SAREA","SLOCATION",
"SRECIPEID","SCUSTOMER","SCUSTPRODUCT","STRACKINTIME",
"STRACKOUTTIME","LTRACKINQTY","SSTARTDATETIME","SDATETIME",
"SUSERID","CFLAG","SCOMMENT","CACTIONFLAG","SGROUPID" FROM
"WALTON"."test_table" "A2"
0 SORT (JOIN)
0 VIEW
0 SORT (UNIQUE)
0 MERGE JOIN
0 SORT (JOIN)
0 REMOTE [!]
SELECT "SO_NO","STATUS","CLOSE_DATE" FROM
"WALTON"."SCORDERD" "A3" WHERE "CLOSE_DATE"<=:1-:2
AND "STATUS"='CLOSE'
0 SORT (JOIN)
0 REMOTE [!]
SELECT "SO_NO","BATCHCARD_NO" FROM
"WALTON"."SORDERM" "A4" WHERE "BATCHCARD_NO"=
'T3027715.11'

.. . The query here is Why the explain plan shows Remote and to me it seems that its taking the entire query to remote site and than executing it. Correct me if I am wrong and What can be done in this scenario to execute the query locally and why the optimizer is not smart enough. The db is running RULE based optimizer.


Tom Kyte

Followup  

July 13, 2004 - 11:51 am UTC

because you are using the rbo and the rbo is not very smart at all - it just uses hard coded rules. it does not known anything about the numbers of rows in tables, data distribution nothing.

look up the driving_site hint (in the performance guide), you may be able to push the query over to the remote site for optimization.

or use the cbo with good statistics in place.

access across DB link

July 19, 2004 - 2:10 pm UTC

Reviewer: Rima Parikh from MN USA

Hello :

I'm trying to write a one time load procedure to read data from a remote table, perform some calculations and store the calculated results in a local table.

The remote table name is dw_mly_funded_loan. It has about 58Million rows with a secondary index on dw_funded_loan_id and primary index on the joined key (dw_funded_loan_date, dw_funded_loan_id). The table has information for each loan_id, for multiple dates (1 to about 40) per loan.

create table DW_MLY_FUNDED_LOAN
(
DW_MLY_FUNDED_LOAN_DATE DATE not null,
DW_FUNDED_LOAN_ID NUMBER not null,
DELQ_REPORT_MBA_DAY NUMBER(6),
DELQ_REPORT_OTS_DAY NUMBER(6)
)

alter table DW_MLY_FUNDED_LOAN
add constraint DW_MLY_FUNDED_LOAN_PK primary key (DW_MLY_FUNDED_LOAN_DATE,DW_FUNDED_LOAN_ID);


create index DW_MLY_FUNDED_LOAN_S01 on DW_MLY_FUNDED_LOAN (DW_FUNDED_LOAN_ID);


I'm trying to write a batch procedure to load data for all loans in the dw_mly_funded_loan table in pl/sql tables ( bulk load of 100 at a time), perform some calculations on each loan with output of one row per loan which is to be stored in my local database table.

create or replace nbr_ty as table of number;

create synonym DW_MLY_FUNDED_LOAN
for DW.DW_MLY_FUNDED_LOAN@DWSH.RFC.COM;

For loading the data in internal pl/sql tables I use the following procedure :

-- tab_SeqIDs is loaded with loan_ids' (100 at a time) and the following procedure is called in a loop

PROCEDURE sp_LoadDelinqData(tab_SeqIds IN NBR_TY, d_CutOffDate IN DATE) AS

BEGIN

SELECT D1.DW_FUNDED_LOAN_ID,
D1.DW_MLY_FUNDED_LOAN_DATE,
NVL(D1.DELQ_REPORT_MBA_DAY, 0),
NVL(D1.DELQ_REPORT_OTS_DAY, 0) bulk collect
into tab_DELQ_FUNDED_LOAN_ID,
tab_DELQ_MLY_FUNDED_LOAN_DATE,
tab_DELQ_REPORT_MBA_DAY,
tab_DELQ_REPORT_OTS_DAY
FROM DW_MLY_FUNDED_LOAN D1
WHERE D1.DW_FUNDED_LOAN_ID in ( select * from table(tab_SeqIds) ) and
(d1.DW_MLY_FUNDED_LOAN_DATE between ADD_MONTHS(d_CutOffDate, -APTYPES_PKG.c_DELINQ_LOOKBACK) and --this is defined as 24
d_CutOffDate)
ORDER BY
D1.DW_FUNDED_LOAN_ID, d1.DW_MLY_FUNDED_LOAN_DATE;

END sp_LoadDelinqData;

I tried to run an explain plan on an equivalent query :
SELECT D1.DW_FUNDED_LOAN_ID,
D1.DW_MLY_FUNDED_LOAN_DATE,
NVL(D1.DELQ_REPORT_MBA_DAY, 0),
NVL(D1.DELQ_REPORT_OTS_DAY, 0)
FROM DW_MLY_FUNDED_LOAN D1
WHERE D1.DW_FUNDED_LOAN_ID in ( select * from table(cast(:tab_SeqIds as nbr_ty)) ) and
(d1.DW_MLY_FUNDED_LOAN_DATE between ADD_MONTHS(sysdate, :b1) and sysdate)
ORDER BY
D1.DW_FUNDED_LOAN_ID, d1.DW_MLY_FUNDED_LOAN_DATE;

SELECT STATEMENT, GOAL = CHOOSE
SORT ORDER BY
FILTER
HASH JOIN
SORT UNIQUE
COLLECTION ITERATOR PICKLER FETCH
REMOTE SELECT "DW_MLY_FUNDED_LOAN_DATE","DW_FUNDED_LOAN_ID","DELQ_REPORT_MBA_DAY","DELQ_REPORT_OTS_DAY" FROM "DW"."DW_MLY_FUNDED_LOAN" "D1" WHERE "DW_MLY_FUNDED_LOAN_DATE">=ADD_MONTHS(:1,TO_NUMBER(:2)) AND "DW_MLY_FUNDED_LOAN_DATE"<=:3


Looks like the optimizer is not able to do the dw_funded_loan_id filtering over at the remote site. So, it ends up filtering only by date and bringing back most of the table and then filtering by the loan_ids. I would like it to ideally filter by the loan ids over at the remote site as in :

SELECT D1.DW_FUNDED_LOAN_ID,
D1.DW_MLY_FUNDED_LOAN_DATE,
NVL(D1.DELQ_REPORT_MBA_DAY, 0),
NVL(D1.DELQ_REPORT_OTS_DAY, 0)
FROM DW_MLY_FUNDED_LOAN D1
WHERE D1.DW_FUNDED_LOAN_ID in ( :l1, :l2, :l3, :l4, :l5 ) and
(d1.DW_MLY_FUNDED_LOAN_DATE between ADD_MONTHS(sysdate, :b1) and --this is defined as 24
sysdate)
ORDER BY
D1.DW_FUNDED_LOAN_ID, d1.DW_MLY_FUNDED_LOAN_DATE

SELECT STATEMENT REMOTE, GOAL = CHOOSE 20 1 150
SORT ORDER BY 20 1 150
INLIST ITERATOR
TABLE ACCESS BY INDEX ROWID 20 1 147 1 DW_MLY_FUNDED_LOAN DWSH.RFC.COM
INDEX RANGE SCAN 145 3 DW_MLY_FUNDED_LOAN_S01 DWSH.RFC.COM NON-UNIQUE


Any help would be greatly appreciated. I apologize if the information is not in the form you'd want or is not sufficient. Please let me know and I will try to provide whatever else is needed. I do not have access to tkprof type information for company policy reasons and just the fact that I havent fought for it yet.

I have read up as much as I could find on your site about this. Tried the driving_site hint and even tried giving it an index hint - no effect. I have a feeling the problem has to do with the dynamic nature of the pl/sql table - tab_SeqIds that can only be determined at run time.

Thanks much for the wonderful help you provide via this site.








Tom Kyte

Followup  

July 19, 2004 - 2:41 pm UTC

are you allowed to create a global temporary table on the remote site? if so, I'd put the data over there and query it up.

Else, since this is a one time process -- use an inlist. you are using 100 elements in that table -- just code

where loan_id in ( array(1), array(2), array(3), ..... array(100) )

and if you have less than 100 elements in the array, pad it out with NULLs

access across db links

July 19, 2004 - 3:13 pm UTC

Reviewer: Rima Parikh from MN USA

Thanks Tom. That was a quick response.

Not sure what you mean by putting data in a global temporary table.

I dont have any other access to the remote site except select. However I could ask for something to be created for me. Are you saying I do the calculation at the remote site and store the calculated columns over there as well?


The second suggestion is possible for the one time load. However I have some further questions on that :
1. Is 100 at a time efficient for 58Million rows? Or would 1000 or 10000 be better? I know you prefer smaller bulks, but I have in other places done bulk's of 1000 and even 10,000 with much better performance than 100.

2. Although this is a one time load, I would like to use a similar procedure to do a monthly batch to load changed/new loans. Also, the calculations are being done for one particular date (sysdate) which is what the users pick 95% of the time. However, for the remaining 5% of the time, I also need to do the calculations at run-time accessing the data across a link at run-time - with the expectation that it will be slow but atleast be some reasonable time.

From one of the suggestions earlier in this chain, I tried the following that had a little better plan, is this something worth pursuing ?

SELECT D1.DW_FUNDED_LOAN_ID,
D1.DW_MLY_FUNDED_LOAN_DATE,
NVL(D1.DELQ_REPORT_MBA_DAY, 0),
NVL(D1.DELQ_REPORT_OTS_DAY, 0)
FROM DW_MLY_FUNDED_LOAN D1, DW_MLY_FUNDED_LOAN D2
WHERE d1.dw_funded_loan_id=d2.dw_funded_loan_id and
D2.DW_FUNDED_LOAN_ID in (select * from table( cast(:tab_SeqIds as nbr_ty))) and
(d2.DW_MLY_FUNDED_LOAN_DATE between ADD_MONTHS(sysdate, :b1) and sysdate)
ORDER BY
D1.DW_FUNDED_LOAN_ID, d1.DW_MLY_FUNDED_LOAN_DATE

SELECT STATEMENT, GOAL = CHOOSE 3024 42 2492
SORT ORDER BY 3024 42 2492
FILTER
NESTED LOOPS 3024 42 2489
HASH JOIN SEMI 24 1 2360
REMOTE 64655822 2938901 829 DWSH.RFC.COM SELECT "DW_MLY_FUNDED_LOAN_DATE","DW_FUNDED_LOAN_ID" FROM "DW"."DW_MLY_FUNDED_LOAN" "D2" WHERE "DW_MLY_FUNDED_LOAN_DATE">=ADD_MONTHS(:1,TO_NUMBER(:2)) AND "DW_MLY_FUNDED_LOAN_DATE"<=:3
COLLECTION ITERATOR PICKLER FETCH
REMOTE 1392 29 129 DWSH.RFC.COM SELECT "DW_MLY_FUNDED_LOAN_DATE","DW_FUNDED_LOAN_ID","DELQ_REPORT_MBA_DAY","DELQ_REPORT_OTS_DAY" FROM "DW"."DW_MLY_FUNDED_LOAN" "D1" WHERE "DW_FUNDED_LOAN_ID"=:1


Tom Kyte

Followup  

July 19, 2004 - 4:42 pm UTC

i'm saying insert:

select * from table( cast(:tab_SeqIds
as nbr_ty))

into the remote table and then query using that remote table instead of the object type.


make it "tunable" if you like -- 100, 500, whatever.


how is that plan 'better'??

access across db link

July 19, 2004 - 4:58 pm UTC

Reviewer: rima parikh from mn usa

Thanks Tom. You're right, I wasnt thinking straight - that plan wasnt any better.

I didnt know about global temporary tables, hence the dumb question. Meantime, I read up a bit on it and since I dont have access to the remote site, here's what I tried :

create global temporary table AP_DELQ_GT --in my local db
(
LOAN_ID NUMBER(10)
)
on commit delete rows;


forall i in 1..tab_SeqIds.count
insert into ap_delq_gt (loan_id) values ( tab_SeqIds(i));

SELECT /*+rule driving_site(d1)*/ D1.DW_FUNDED_LOAN_ID,
D1.DW_MLY_FUNDED_LOAN_DATE,
NVL(D1.DELQ_REPORT_MBA_DAY, 0),
NVL(D1.DELQ_REPORT_OTS_DAY, 0) bulk collect
into tab_DELQ_FUNDED_LOAN_ID,
tab_DELQ_MLY_FUNDED_LOAN_DATE,
tab_DELQ_REPORT_MBA_DAY,
tab_DELQ_REPORT_OTS_DAY
FROM DW_MLY_FUNDED_LOAN D1, ap_delq_gt gt
WHERE gt.LOAN_ID = d1.DW_FUNDED_LOAN_ID and
(d1.DW_MLY_FUNDED_LOAN_DATE between ADD_MONTHS(d_CutOffDate, -APTYPES_PKG.c_DELINQ_LOOKBACK) and
d_CutOffDate)
ORDER BY
D1.DW_FUNDED_LOAN_ID, d1.DW_MLY_FUNDED_LOAN_DATE;

that gave the following plan and seems to be working, I'm running it right now :

SELECT STATEMENT REMOTE, GOAL = HINT: RULE
SORT ORDER BY
TABLE ACCESS BY INDEX ROWID DW_MLY_FUNDED_LOAN DWSH.RFC.COM
NESTED LOOPS
REMOTE ! SELECT "LOAN_ID" FROM "AP_DELQ_GT" "A1"
INDEX RANGE SCAN DW_MLY_FUNDED_LOAN_S01 DWSH.RFC.COM NON-UNIQUE

I dont like the use of the rule hint to get it to use the index. I know this is a very generic question but, If I do get the temporary table created in the remote db, is it likely to use the index without having to hint it?

Tom Kyte

Followup  

July 19, 2004 - 5:01 pm UTC

what you should try first is:

o use dbms_stats.set_table_stats to set the number of rows to 100 and the number of blocks to one for this gtt.

o drop the rule hint

o keep the driving site hint


problem is the optimizer will default the number of rows to some very large number, dbms_stats can be used to work around that.

access across db link

July 19, 2004 - 5:09 pm UTC

Reviewer: Rima Parikh from mn usa

Cool! Thanks, that would be perfect.

I dont quite know how to use the dbms_stats, but will read up and try it out.

Thanks again.

Query fast but insert slow

August 16, 2004 - 10:23 am UTC

Reviewer: A reader

I have the following fully remote query

--------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Inst |
--------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT REMOTE | | | | | |
| 1 | FILTER | | | | | |
| 2 | NESTED LOOPS OUTER | | | | | |
| 3 | NESTED LOOPS OUTER | | | | | |
| 4 | NESTED LOOPS OUTER | | | | | |
| 5 | TABLE ACCESS BY INDEX ROWID| S_EVT_ACT | | | | PP704 |
| 6 | INDEX UNIQUE SCAN | S_EVT_ACT_P1 | | | | PP704 |
| 7 | TABLE ACCESS BY INDEX ROWID| S_ORG_GROUP | | | | PP704 |
| 8 | INDEX UNIQUE SCAN | S_ORG_GROUP_P1 | | | | PP704 |
| 9 | TABLE ACCESS BY INDEX ROWID | S_ASSET | | | | PP704 |
| 10 | INDEX UNIQUE SCAN | S_ASSET_P1 | | | | PP704 |
| 11 | TABLE ACCESS BY INDEX ROWID | S_EVT_ACT_X | | | | PP704 |
| 12 | INDEX RANGE SCAN | S_EVT_ACT_X_U1 | | | | PP704 |
--------------------------------------------------------------------------------------------

Note: fully remote operation, rule based optimization

(Yes, it uses the 6-letter application I know you dont like! :)

This query returns one row, it is very fast (it goes by the Siebel's internal row-id)

But when I do a

create table t as <that query>, the plan changes to

--------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost | Inst |IN-OUT|
--------------------------------------------------------------------------------------
| 0 | CREATE TABLE STATEMENT | | | | | | |
| 1 | LOAD AS SELECT | | | | | | |
|* 2 | FILTER | | | | | | |
| 3 | MERGE JOIN OUTER | | | | | | |
| 4 | SORT JOIN | | | | | | |
| 5 | MERGE JOIN OUTER | | | | | | |
| 6 | SORT JOIN | | | | | | |
| 7 | MERGE JOIN OUTER| | | | | | |
| 8 | SORT JOIN | | | | | | |
| 9 | REMOTE | | | | | SIEBE~ | R->S |
|* 10 | SORT JOIN | | | | | | |
| 11 | REMOTE | | | | | SIEBE~ | R->S |
|* 12 | SORT JOIN | | | | | | |
| 13 | REMOTE | | | | | SIEBE~ | R->S |
|* 14 | SORT JOIN | | | | | | |
| 15 | REMOTE | | | | | SIEBE~ | R->S |
--------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - filter(1=2)
10 - access("A"."ROW_ID"="X"."PAR_ROW_ID"(+))
filter("A"."ROW_ID"="X"."PAR_ROW_ID"(+))
12 - access("A"."ORG_GROUP_ID"="G"."ROW_ID"(+))
filter("A"."ORG_GROUP_ID"="G"."ROW_ID"(+))
14 - access("A"."ASSET_ID"="B"."ROW_ID"(+))
filter("A"."ASSET_ID"="B"."ROW_ID"(+))

Note: rule based optimization

This is dog slow!

Why the dramatic change in plans between the two? Because of this, I am forced to resort to slow-by-slow processing instead of set-based operations.

Help!

Thanks

Tom Kyte

Followup  

August 16, 2004 - 7:38 pm UTC

can you two step it.. the CTAS may be precluding the remote optimization as it must do a lot of local processing to create that table.

ctas where 1=0;

insert into select ...;

Query fast but insert slow

August 16, 2004 - 8:41 pm UTC

Reviewer: A reader

I already tried that, the INSERT is slow as well.

I finally did the following:

CTAS where 1=0
insert into
select /*+ driving_site(siebel.s_evt_act) */ ....

This works very fast. I guess the hint pushes the query optimization over to the remote site (which is still RBO since Siebel doesnt support CBO yet) and then the results of the query are shipped over the wire to be inserted.

Thanks

Db links!!!!!!!

August 18, 2004 - 11:40 am UTC

Reviewer: A reader

Hi Tom,
Can we create a view in a test server which references a table in production.
For example a view like:
select * from table@production.
We tried it but after compilation of the view the link disappears.
Any suggestiosn as to how can this be achieved. I know we can go for MV's or replication of the above-mentioned table.
But is it feasible using views with db links.
Thanks
Paola Andrea


Tom Kyte

Followup  

August 18, 2004 - 11:50 am UTC

"the link disappears"????

what do you mean by that.

yes, you can definitely create a view as select * from t@dblink, do it all of the time, works as advertised. you'd need to supply an example here showing exactly what you mean.

Example

August 18, 2004 - 12:06 pm UTC

Reviewer: A reader

Sorry Tom for putting and incomplete question.
The view is created as:
select * from tablename@production

But after it is compiled it changes to:
select * from tablename
and hence references the local table.
Thanks again


Tom Kyte

Followup  

August 18, 2004 - 12:19 pm UTC

nope, sorry - doesn't work that way.

cut and paste the entire example, just like this:

ops$tkyte@ORA9IR2> create database link loopback@ora9ir2
  2  using 'ora9ir2';
 
Database link created.
 
ops$tkyte@ORA9IR2> create view v as select * from dual@loopback@ora9ir2;
 
View created.
 
ops$tkyte@ORA9IR2> select text from user_views;
 
TEXT
-------------------------------------------------------------------------------
select "DUMMY" from dual@loopback@ora9ir2
 



prove to me what you say is happening.  show me step by step by step how to "reproduce" 

Accessing without db links

September 02, 2004 - 11:19 am UTC

Reviewer: oracleo from IN

Hi Tom,

There was a brief discussion at our place during which a guy suggested that we can access remote database tables without using DB Links !!

Is it possible.

Please suggest

Thanks

Tom Kyte

Followup  

September 02, 2004 - 11:21 am UTC

not using "SQL" it isn't.

i could write a java stored procedure that used jdbc to open a new connection and ran a query...

i could use utl_http to run a url on a web server that connects to another database and get information back....

there are thousands of ways perhaps, but none of the are "SQL"

so, you'd have to be more specific.

Database link problem

September 17, 2004 - 5:31 pm UTC

Reviewer: venkat from NY,USA

I have below procedure in Schema A.
Process_id column of process_info is a primarykey.

create or replace procedure test_link(o_ref OUT sys_refcursor) is
begin
   OPEN    o_ref FOR
           'Select x.process_id FROM process_info@tlink x,
             pa_Exceptions e WHERE x.process_id=e.process_id';
end test_link;
 
then i give 
  grant execute on test_link to b;

In Schema B:
i create a snyonym for test_link as 
create synonym test_link for a.test_link;

then when i execute the procedure in schema b, and trying to get data from the ref cursor , its giving "connection description for the remote database found". 

SQL> variable y refcursor
SQL> exec test_link(:y);

PL/SQL procedure successfully completed.

SQL> print y
ERROR:
ORA-02019: connection description for remote database not found



no rows selected

SQL> 

whereas if the join in the procedure is changed its able to fetch the records .

Can you please clarify why its happening like that.




 

Tom Kyte

Followup  

September 17, 2004 - 8:10 pm UTC

changed how?

database link

September 18, 2004 - 10:37 am UTC

Reviewer: VenkatRamanan from NY,USA

i changed the procedure using the detail table of "process_info" and its working from schema B.

create or replace procedure test_link(o_ref OUT sys_refcursor) is
begin
OPEN o_ref FOR
'Select distinct x.process_id FROM process_detail@tlink x,
pa_Exceptions e WHERE x.process_id=e.process_id';
end test_link;


Tom Kyte

Followup  

September 18, 2004 - 10:57 am UTC

create database link tlink .......

show me the entire thing from start to finish -- create or replace procedure p1, p2 (one you say works, the other that doesn't), grant, connect as the other user, run them

CUT AND PASTE

NO EDITS ALLOWED...

September 20, 2004 - 10:22 am UTC

Reviewer: VenkatRamanan from NY,USA

As asekd , i am sending you the full information tom.

In Schema ITIT
--------------
SQL> DESC PROCESS_INFO
Name                Type         Nullable Default Comments 
------------------- ------------ -------- ------- -------- 
PROCESS_ID          NUMBER                                 
NT_LOGIN            VARCHAR2(20) Y                         
APP_ID              VARCHAR2(10) Y                         
PROCESS_TYPE        VARCHAR2(30) Y                         
PROCESS_STATUS      CHAR(1)      Y                         
PROCESS_DESCRIPTION XMLTYPE      Y                         
PROCESS_START_DATE  DATE         Y                         
PROCESS_END_DATE    DATE         Y   

SQL> desc process_Detail
Name             Type      Nullable Default Comments 
---------------- --------- -------- ------- -------- 
PROCESS_ID       NUMBER    Y                         
PROCESS_STEP     NUMBER(2) Y                         
STEP_DESCRIPTION XMLTYPE   Y                         
STEP_STATUS      CHAR(1)   Y                         
STEP_START_TIME  DATE      Y                         
STEP_END_TIME    DATE      Y     



In Schema ITITDM
----------------
 create database link sny.WORLD
  connect to ITIT identified by ITIT
  using 'sny.world';

SQL> desc pa_exceptions
Name           Type          Nullable Default Comments 
-------------- ------------- -------- ------- -------- 
ID_NO          NUMBER(10)    Y                         
PROJ_ID        VARCHAR2(10)  Y                         
RATE_CODE      VARCHAR2(2)   Y                         
EMP_ID         VARCHAR2(10)  Y                         
EMP_NAME       VARCHAR2(40)  Y                         
HRS_WORKED     NUMBER(10,3)  Y                         
PERSON_DAYS    NUMBER(10,3)  Y                         
WEEK_END_DATE  DATE          Y                         
PROCESS_ID     NUMBER(10)    Y                         
PERSON_TYPE    CHAR(1)       Y        'E'              
EXCEPTION_NOTE VARCHAR2(500) Y             

SQL> create or replace procedure test_link(o_ref OUT sys_refcursor) is
  2  begin
  3     OPEN    o_ref FOR
  4             'Select x.process_id FROM process_detail@sny.world x,
  5               pa_Exceptions e WHERE x.process_id=e.process_id';
  6  end test_link;
  7  /

Procedure created.

SQL>  VARIABLE Y REFCURSOR
SQL>  EXEC TEST_LINK(:Y);

PL/SQL procedure successfully completed.

SQL> PRINT Y

PROCESS_ID
----------
        43

I now grant the execute privilege to the user ITITDM_USR through the role ITITDM_EXEC_ROLE. This role is already given to the ITITDM user.

SQL> Grant execute on test_link to ITITDM_EXEC_ROLE;

Grant succeeded.

IN ITITDM_USR
-------------
SQL> conn ititdm_usr/ititdm_usr@dnyitit2.world
Connected.
SQL> create synonym TEST_LINK
  2    for ITITDM.TEST_LINK;

Synonym created

SQL> VARIABLE Y REFCURSOR
SQL> EXEC TEST_LINK(:Y);
SQL> print y
ERROR:
ORA-02019: connection description for remote database not found



no rows selected

SQL> 

Sorry tom.. When i did with the detail table also , i am getting the error. Can you please clarify why its happening like that.

 

Tom Kyte

Followup  

September 20, 2004 - 11:03 am UTC

and how did the other guy connect -- this is why I want a *cut and paste* from start to finish, without edits.

did the other guy connect the same.


do this:

sql> connect as owner of procedure
sql> show procedure working
sql> connect as other guy
sql> show procedure not working

cut and paste the entire thing

How is the performance of DB links

October 14, 2004 - 5:34 pm UTC

Reviewer: Raju

On a DW project that I am working on the source systems send data and sometimes it takes them more than 10 hours to send 10K records. The reason given is that we join two databases - one in US and the other in Europe. Both the database tables have similar number of records - one in Europe has 20K records and the other in US has 30K records. What the query is doing (as I am told) is picking a Purchase order number from the database table in Europe and then picking up the associated attribute from the database table in USA.
They are not ready to provide the trace/Explain plan and hence I cannot forward that to you. They tell me that if both the databases were in th USA it would be faster. I do not agree but need an experts opinion.
My questions are:
Are database links evil? Performance wise.
Should we create local views(materialized) and then use that instead of a remote table.
Is there a way that the query be written such that instead of getting one purchase order from database table in Europe and then picking up the associated attribute from the database table in USA, it does it more smartly like in bulk?
How to measure the performance? TKPROF?
I am not a database person so please help.

Thanks
Raju



Tom Kyte

Followup  

October 14, 2004 - 7:56 pm UTC

dblinks are neither evil, nor pure good.

they are -- a tool.

so, copy the UK table to the US over the dblink and see how that performs.

Just to clarify

October 14, 2004 - 8:45 pm UTC

Reviewer: Raju

Tom,
Just wanted to know that you want me to run a command like
create table <in US database>
AS select * from <table in UK database>@dblink

and then run the current query without the database.

Do you think the WHERE clause in the current query is killing the performance?

Thanks
Raju

Tom Kyte

Followup  

October 15, 2004 - 10:52 am UTC

create a global temporary table, insert into it as select * from the other table, join to that.

If that is significantly "faster", perhaps that is the option you want to use.

if it is not significantly faster -- then well, it is taking a long time to get your data over your link.

TEST CONNECTION

November 02, 2004 - 6:09 pm UTC

Reviewer: Neeraj Nagpal from Los Angeles, CA

Tom,

How can I check the validity of a Oracle UID/PWD. This is just to check the validity only and not to actually connect using the passed UID/PWD. This validity check needs to be called from the PL/SQL, I have been thinking of using the datbase links to do this, but I don't know exactly how to do it. or is there a function available to do this ?


Thanks Always for your Help.
Neeraj


Tom Kyte

Followup  

November 03, 2004 - 6:42 am UTC

search for

check_password



connecting from 9i to 7.3.4

November 05, 2004 - 2:04 pm UTC

Reviewer: Eugene

Hi Tom,
I am trying to retrieve some data into 9i from 7.3 running the following query (that fails)
SELECT MAX(seq)+1 INTO sbatchid FROM intlog@LINK_TO_7X.US.UB.COM;

I contacted my DBA and she told me: There is no workaround as this is an unsupported combination.

Is there anything I can do to resolve it?

Thanks,

Tom Kyte

Followup  

November 05, 2004 - 5:42 pm UTC

9ir2 is explicity "not working against v7.3". It totally doesn't work pretty much. Many issues.

Typcast variables across the DB Link.

November 29, 2004 - 11:54 am UTC

Reviewer: MSU from India

Dear Tom,

Assume the following situation.

I have a Database say DB_1 and I have another Database called DB_2.

I create a link for DB_1 and in DB_2 I run a script.

In the the declarative section of the script I declare as follows

Table_Name.<COLUMN NAME>%TYPE (Table_Name is a table in DB_1)

I wish to know whether typcast of variables across the DB Link is possible or not as mentioned above.

Tom Kyte

Followup  

November 29, 2004 - 3:30 pm UTC

ops$tkyte@ORA9IR2> declare
  2          l_x t.x@ora9ir2%type;
  3  begin
  4          null;
  5  end;
  6  /
 
PL/SQL procedure successfully completed.
 

I prefer to use VIEWS of T@ora9ir2 myself -- so my stored code is dependent on the view and when it recompiles it doesn't need to access the dblink just to do that.  It uses the dictionary information about the view to recompile (makes recompilation lots faster) 

re:connecting from 9i to 7.3.4

November 29, 2004 - 3:36 pm UTC

Reviewer: Jeff from Oak Creek, WI USA

If you're REALLY desperate to link a 9ir2 database with a 7.3 database, if you have any 8i databases lying around you could try to "hop" through an intermediate. 9i will talk to 8i, and 8i will talk to 7.3. I'm certain performance would be "suboptimal" (to say the least!), but you could probably make it work.

Db links from 9 to 7

November 29, 2004 - 4:05 pm UTC

Reviewer: veera from rockville, MD

We did exactly the same. We created a synonym using a DB link from 9 to 8 (staging DB) and another synonym (with the same name) from 8 to 7. It works fine most of the cases except in case of insert into select * which gives Oracle error ORA-00600: internal error code, arguments: [qctstc2o1], [1], [0], [1], [1], [30], [30], []. We did work around this by splitting.

use synonym for db link.

November 29, 2004 - 5:21 pm UTC

Reviewer: Sean from NJ, USA

Hi Tom,

You mentioned using view instead of using db link in the code. We actually use synonym instead of using db link directly. Which one is better in terms of performance and compilation. (Oracle 9204)

Thanks so much for your help.



Tom Kyte

Followup  

November 29, 2004 - 7:09 pm UTC

views

when you


create view t as select * from t@remote;

you populate your local data dictionary -- so a procedure like:

create procedure p
as
begin
for x in ( select * from t ) loop...


doesn't need to touch the database link to compile or anything. However, if you

create synonym t for t@remote;

it will have to open the database link just to compile. I like the views.

Performance over db links

December 09, 2004 - 2:35 pm UTC

Reviewer: A Reader from BG

Tom,

Assuming i access my PROD database from a STAGING area over a db link - would that in any way affect the functioning of my PROD database?

Thanks,

Tom Kyte

Followup  

December 09, 2004 - 3:32 pm UTC

not anymore than if you just logged into prod directly and did stuff.

ORA-00904 - view over db link

December 29, 2004 - 7:07 am UTC

Reviewer: Thiyag from Chennai, India

Hi Tom,
I have a view (the exact SQL being a lengthy one) with db link retriving around 30 columns. When I select only from this view it works fine and gives me the expected results, but when I try to join this view with an existing table it pops up the error message invalid identifier "ORA-00904:A3.col_30". I removed the rest 29 columns from the view and put in only the col_30 and it works fine when I join with the table. (I was trying to simulate this error with emp and dept tables so I can give you the cut paste code to reproduce but it works fine with those tables. Trying to figure out some other way so that I can give you the cut paste code). Appreciate if you could provide me with pointers or work around to get rid of this error.

Tom Kyte

Followup  

December 29, 2004 - 10:11 am UTC

You'll need to work with support on this one -- they can help you set some trace events to collect more information.

Insert not using Driving_Site

December 31, 2004 - 12:25 pm UTC

Reviewer: Jasbir Kular from Toronto, Canada

I have a query that has 3 remote tables and 2 local tables. I use the driving_site hint to push the query to the remote database. It works great when the query runs by itself but when I add an insert to the query (INSERT INTO ... SELECT FROM <remote tables>) the plan shows that the query is not executed remotely. Why does this happen?

Here is the plan for the query without the insert:

SELECT STATEMENT REMOTE Optimizer Mode=CHOOSE 16 33188
NESTED LOOPS 16 3 K 33188
NESTED LOOPS 16 2 K 33156
NESTED LOOPS 1 110 5
NESTED LOOPS 1 96 3
TABLE ACCESS FULL GL.GL_SETS_OF_BOOKS 1 47 2 AFRG01D2.US.ORACLE.COM
REMOTE 1 49 1 ! SERIAL
REMOTE 4 56 2 ! SERIAL
TABLE ACCESS BY INDEX ROWID GL.GL_BALANCES 469 34 K 33151 AFRG01D2.US.ORACLE.COM
INDEX RANGE SCAN GL.GL_BALANCES_N2 297 K 1233 AFRG01D2.US.ORACLE.COM
TABLE ACCESS BY INDEX ROWID GL.GL_CODE_COMBINATIONS 1 66 2 AFRG01D2.US.ORACLE.COM
INDEX UNIQUE SCAN GL.GL_CODE_COMBINATIONS_U1 1 1 AFRG01D2.US.ORACLE.COM

Here is the plan for the query with the insert:

INSERT STATEMENT Optimizer Mode=CHOOSE 69 25893
LOAD AS SELECT
NESTED LOOPS 69 19 K 25893
NESTED LOOPS 69 12 K 25755
NESTED LOOPS 1 114 5
MERGE JOIN CARTESIAN 1 100 3
TABLE ACCESS BY INDEX ROWID XXTEMP.SYNC_CONTROL_T 1 49 1
INDEX RANGE SCAN XXTEMP.SOB_CONTROL_PK 1 2
BUFFER SORT 1 51 2
REMOTE 1 51 2 APPS.CLARICA.COM SERIAL
TABLE ACCESS FULL XXTEMP.SYNC_BALANCE_TYPE_RULES_T 4 56 2
REMOTE 2 K 151 K 25750 APPS.CLARICA.COM SERIAL
REMOTE 1 102 2 APPS.CLARICA.COM SERIAL


Thanks for your help.

Tom Kyte

Followup  

December 31, 2004 - 12:30 pm UTC

the insert will make this a local operation -- if you create a remote view that joins the tables over there -- then the view will have to be optimized at the remote site and your query becomes:

insert into local-table select * from view_defined@remote_site;

Insert not using Driving_Site hint

December 31, 2004 - 12:27 pm UTC

Reviewer: Jasbir Kular from Toronto, Ontario

Sorry, I forgot to add in that I am using version 9.2.0.5.

Thanks.

DBLINK from 7.3 to 9i

January 11, 2005 - 6:44 am UTC

Reviewer: Jignesh from London

I have got Oracle Datawarehouse Builder 9i and I want to fetech the data from 7.3 (rightnow can not upgrade to latest version due to some limitations).

I am trying to create dblink between two databases.. but as per my understanding I can not access 7.3 database using dblink in 9i.. is that right? what is the otherwayround for that?



Tom Kyte

Followup  

January 11, 2005 - 10:31 am UTC

9ir2 and above explicitly do not support connections to or from 7.3.

the only thing i've heard of is to use a man in the middle, put an 8i instance between you and 7.3. Not sure how it would perform personally.

Just thought of something else -- haven't tried it, but hey:

</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:4406709207206#18830681837358 <code>

if you can dig up a 7.3 odbc driver, you might be able to do that.

Interesting

January 13, 2005 - 9:45 am UTC

Reviewer: jignesh from London

Your answer is really interesting... I need to convice my seniors for this. They are more interested in linking 9i to 7.3 through 8i. Would definitely update this if connectivity through DSN successful.


ora-12640

January 18, 2005 - 11:48 am UTC

Reviewer: Nishant from india

Sir,

i have created the db link with 
SQL>CREATE DATABASE LINK TOCMSS.HFCLCONNECT.COM CONNECT TO CALLCENTER IDENTIFIED BY <PWD> USING 'cmss.hfclconnect.com';

created successfully

SQL>select * from dual@tocmss;
ORA-12535: Operation Timed Out

i changed the 
SQLNET.AUTHENTICATION_SERVICES= (NTS) to NONE

SQL>select * from dual@tocmss;
ERROR at line 1:
ORA-12640: Authentication adapter initialization failed

searched a lot but unable to find solid resolution 

please suggest .. how to resolve it..

Thanks in advance 

Tom Kyte

Followup  

January 18, 2005 - 12:57 pm UTC

comment out the authentication services.

ora-12640

January 19, 2005 - 5:25 am UTC

Reviewer: nishant

Sir,
sorry cann't get you . can you please eleborate



Tom Kyte

Followup  

January 19, 2005 - 10:44 am UTC

#SQLNET.AUTHENTICATION_SERVICES= (NTS) to NONE
^^

comment it out

albert

January 19, 2005 - 10:15 pm UTC

Reviewer: albert from china

Hi tom

you say you prefer to plsql rather than pro*C,
But I have a case in our Data Warehouse system as following:
1/ a source table "sales_source" with 30+ million records :
column
--------
prod_id
cust_id
date_id
sales_amount

2/ and two Dimension tables
2.1/ the "Customer" table with 2+ million records:
column
---------------------
cust_Surrogate_key
cust_id
cust_name
cust_age

2.2/ the "product" table with 2000 records:
column
--------------------
prod_Surrogate_key
prod_id
prod_name
prod_catalog

3/ the target fact table "cube_sales" is
column
--------------
cust_Surrogate_key
prod_Surrogate_key
date_id
sales_amount

We want to transfer sales data from the source table to the target one, meanwhile replacing the cust_id with a Surrogate key such that we could resolve the "Slowly Changing Dimensions" problem.
Would you please show me a simple and effective PL/SQL solution to achive the that ? I wonder if PL/SQL can be enough powerful to do faster lookup then pro*C ?


best regard



Tom Kyte

Followup  

January 20, 2005 - 10:16 am UTC

take your procedural c code and do the same thing in plsql. they are just procedural languages?

I would be tempted to not look for a PLSQL solution, but rather a SQL solution -- but that is up to you. Use bulk collects and forall i processing where in c you would have used host arrays....

Timeout "timer" reset

February 10, 2005 - 2:11 pm UTC

Reviewer: A reader from Florida

Tom,

I have a stored procedure that inserts data in a table selecting from a remote table using a cursor loop. I modified the procedure to eliminate the cursor and just issue a single insert/select. When I run the procedure it fails with an ORA-03113 end-of-file communication channel error.

The single insert/select takes about 20 minutes to run. The CONNECT_TIMEOUT parameter was set to 5 minutes and was changed to 30 minutes.

The old version of the stored procedure that used a cursor never ran in less than 5 minutes (ran in about 25 minutes). My question is, how come we didn't hit the timeout error before? Did the timeout "timer" get reset on every fetch?

Tom Kyte

Followup  

February 11, 2005 - 7:28 pm UTC

please contact support for 3113, 600 errors.

DB LINK SESSION

February 11, 2005 - 3:59 pm UTC

Reviewer: Push.. from NJ, USA

Tom,
Is there a way to find out if a session in an instance
has opened a db link session in the remote instance.

For example,

In instance DB1, session 1 is querying a table in remote
instance DB2 through a database link. So there is a new
session created in DB2 on befalf this session 1 in DB1.

When there are multiple sessions created in DB2 through
the database link from DB1, Is there a way to map the sessions in DB1 to sessions in DB2.

SID 11 in DB2 is created by SID#1 in DB1
SID 12 in DB2 created by by SID#2 in DB1.

The OSUSER column in V$SESSION will be same in both the
instances for those corresponding sessions.

Is there anything else ?

Thanks
Push..

Tom Kyte

Followup  

February 12, 2005 - 12:11 pm UTC

not as far as I know, they are just sessions -- they could have been logged in via sqlplus (not as a dblink) for all the remote database cares.

sid#1 in db1 would have to pass that sort of information over (and they can, by calling dbms_application_info@remote_site and using the set_client_info routine.

February 16, 2005 - 12:31 pm UTC

Reviewer: A reader

Hi Tom,

Consider my situation and advise accordingly.

I have a database db1 on machine M1 and database db2 on machine M2. Both these machines are in a remote site and I cannot see the desktop of these 2 machines. But I can remotely see another machine M3 which is on the same network as machines M1 and M2. Now assuming I know the tnsnames.ora entry in M1 to connect to M2, can I login to
M3 and create a link from M1 to M2 or shud I execute the 'create database link' statement only directly on M1. Pls help me on this.

Thanks.

Tom Kyte

Followup  

February 16, 2005 - 2:38 pm UTC

confusion on my part. when you are "on m3" what exactly would you be typing "create database link" into?

You can log into m3, and assuming there is some client software -- say sqlplus installed on m3, you can use that to connect to either of db1 and db2 and create database links to any other machine you like.

Some more clarifications needed

February 17, 2005 - 1:23 am UTC

Reviewer: Sanjaya Balasuriya from Colombo, Sri Lanka

Hi Tom,

I'm using 9iR2.
My database is PANDA.
I haven't created a loopback link "PANDA". (actually I can't.)

But still my select; "select * from global_name@panda;" works.

I couldn't find any explanations on this syntax on SQL reference doc. also.
Can please explain what happens here.

Thanks in advance.

Tom Kyte

Followup  

February 17, 2005 - 8:34 am UTC

it is just implied. It is there. You actually don't need database links at all if global names are database names and everything uses "defaults", they are implicit if you have an account on the other database (in your case, the same database in this instance)

Difference between explicit and implicit links

February 17, 2005 - 10:12 am UTC

Reviewer: Sanjaya Balasuriya from Colombo, Sri Lanka

Hi Tom,

Thanks.

And what is the difference between explicit and implicit links ? Through implicit links we can access only our own schema ?
They can not be make public ?

Thanks in advance.

Tom Kyte

Followup  

February 17, 2005 - 1:17 pm UTC

they are just like an explicit link created without a user/password (they are not a proxy link). they use your identity.

Little more clarifications needed

February 17, 2005 - 11:22 pm UTC

Reviewer: Sanjaya Balasuriya from Colombo, Sri Lanka

Hi Tom,

You say;
"You actually don't need database links at all
if global names are database names and everything uses "defaults", they are
implicit if you have an account on the other database (in your case, the same
database in this instance)".

What are the thing that should use defaults ? Listener name and port ?

And I have 2 databases "PANDA" (on HP-UX) and "TUSKER" (on RedHat Linux). In both databases there is a user called "SAN" with same password.
Then I should be able to query "select * from tab@tusker" from SAN@PANDA without creating a database link to TUSKER no ?
But it give ORA-02019. I also have add an entry in tnsnames.ora on PANDA server.

And can tell where this is explained in the documentation also ?


Thanks in advance.

Tom Kyte

Followup  

February 18, 2005 - 7:47 am UTC

I never use them, I explicitly create dblinks, that would be my suggestion.

create the links.

Q on db links

February 18, 2005 - 12:17 pm UTC

Reviewer: A reader

In any of the earlier versions of Oracle, did Oracle ever execute a query that involves a table at remote database
by making a local copy into the local database and
then executing it? I suspect not but wanted to ask if
there was anything similar to this in an earlier version
of Oracle..

Tom Kyte

Followup  

February 18, 2005 - 2:54 pm UTC

we do that today sometimes in effect. we might have to ship an entire table or result of a query from server A to server B in order to finish the query on server B. We'd use temp space as needed to stash the data. That has always been true.

Even today we'll create temporary tables if needed to process a query -- distributed or not.

thank you

February 18, 2005 - 2:58 pm UTC

Reviewer: A reader

"Even today we'll create temporary tables if needed to process a query --
distributed or not."
Do you mean "global temporary tables"?

Tom Kyte

Followup  

February 18, 2005 - 3:18 pm UTC

no, they would be very similar but you won't necessarily seem them in the dictionary (you will for somethings but not for a query)

February 19, 2005 - 4:12 am UTC

Reviewer: Alberto Dell'Era from Milan, Italy

>Even today we'll create temporary tables if needed to process a query

Is it true that (temporary) indexes may get created on them "on the fly" also, or is that a myth ?

And this kind of temp tables are the result of the VIEW row source operation, correct ?

TIA (good old USENET jargoon, not IM speak - the "Fair Warning" doesn't apply ;)

Tom Kyte

Followup  

February 19, 2005 - 8:21 am UTC

well, they might be "hashed" or "sorted" and we generate bitmap indexes on the fly even for 'real' tables.

not only the "view" row source operation. see </code> http://www.dbazine.com/jlewis6.shtml <code>for an example, look for transformation on that page.


(for the longest time, I thought TIA -- thanks in advance -- was like "ciao" or "ta-ta for now" or "goodbye" in some other language :)

Trigger bidirectional

February 23, 2005 - 2:04 pm UTC

Reviewer: David Pujol from Barcelona (Catalonia)

Hi Tom,

I have 2 databases (A and B). Database A has a table A1 and database B has the same table A1. I'd like update these tables online (insert in database A must propagated to database B and the same with updates and deletes). This propagation must be bidirectional (database A --> database B and database B --> database A)

Can you show me ...., how can I implement this approach?, .. triggers? ...

A lot of thanks

Atentament
David Pujol


Tom Kyte

Followup  

February 24, 2005 - 5:07 am UTC

oh my, why have two databases at all here?????

they both must be up
they both must be available

this is an utterly bad idea.... I won't go into how to do it, but you can read the replication guides, they talk of syncronous replication -- but it is the worst thing you could do.


seems like you really want a single database, having two would be a really bad idea.

Trigger bidirectional

February 24, 2005 - 12:05 pm UTC

Reviewer: David Pujol from Barcelona (Catalonia)

Hi Tom,

I know that is a bad idea ..., we have performance problems caused for dblink waits. In future, there will be a unique database, but now is not possible :-(.

I just want duplicate one table ...

Can you explain me how can I know if session procedence is a dblink?

A lot of thanks again.

Tom Kyte

Followup  

February 24, 2005 - 5:05 pm UTC

did you read the above? I pointed you to documentation.

read chapter 1 of the advanced replication guide. I cannot in good faith say much more because you are doing something i totally do not believe in.

reader

March 15, 2005 - 7:11 am UTC

Reviewer: A reader

At a local database, when a database link is used to
access a table from a remote database,

It seems that the SELECT query is seen in the
v$transaction and use rollback segments. However,
the SELECT statement does not show in the
v$sqlarea.sql_text. Is this normal or am I missing
something


Tom Kyte

Followup  

March 15, 2005 - 8:22 am UTC

you can see a sql query in v$transaction?

it is in v$sql/sqlarea -- if there is SQL running, it is there.

Reader

March 15, 2005 - 8:34 am UTC

Reviewer: A reader

I saw sessions in the v$transaction that was consuming
RBS. Could not find SQL from v$sqlarea mapping
taddr, sql_address etc.

I would like to know if database link transactions,
even if it is a SELECT query, use RBS and consume
RBS

Tom Kyte

Followup  

March 15, 2005 - 8:51 am UTC

perhaps that session just wasn't active at the point in time you looked.

Session on remote DB

March 18, 2005 - 11:24 am UTC

Reviewer: Naresh from Cpyrus

Hi Tom,

One of the posts above mentions a session created on the remote DB when a remote object is accessed.

How long does the remote session remain in effect. Is it as long as the local session is active or is there some timeout for the remote session?

Thanks.
naresh

Tom Kyte

Followup  

March 18, 2005 - 11:25 am UTC

until you either

a) close the database link (alter session)
b) exit your session

script for db links

April 05, 2005 - 10:15 am UTC

Reviewer: Pravesh Karthik, india

Tom,

Is there a way to get the db link script generated from database for the existing dblinks ? ..

we have 150 database and each would have atleast 5 to 10 db links.I use dbms_metadata for tables or procedures. can you point to any link or a method how i can go about getting the script generated.

Thanks for your time and consideration,

Pravesh Karthik


Tom Kyte

Followup  

April 05, 2005 - 12:16 pm UTC

the view dba_db_links has most of what you need, sys.link$ everything if you need the password.

should be fairly easy to write the sql.

Using insert over DB link from MS Access to Oracle is slow

April 11, 2005 - 10:15 am UTC

Reviewer: Gu Wang from Canada

Hi Tom,

A DB link oem_to_access is created, which links to a MS access database. When running

insert into gis_transf.MAGENTA_PI_NAME_MASTER (
ROLL, SEQUENCE, NAME, IDENTIFIER, BIRTH_YEAR, BIRTH_MONTH, OCCUPANCY_STATUS, RESIDENCY_CODE)
select ROLL, SEQUENCE, NAME, IDENTIFIER, BIRTH_YEAR, BIRTH_MONTH, OCCUPANCY_STATUS, RESIDENCY_CODE
from PI_NAME_MASTER@oem_to_access;

it needs about one hour to finish 185266 rows. My question is how can make the insert faster?

Oracle database is on version 9.2.0.1 on Windows NT SP6. MS access(97) is on the same machine.



Tom Kyte

Followup  

April 11, 2005 - 10:21 am UTC

guess I would first turn on the 10046 level 12 trace, and run it with "where rownum <= 1000" just to see what the major wait events could be.



Gu Wang

April 11, 2005 - 2:35 pm UTC

Reviewer: denni50 from na

Make sure you have set up a primary key on the Access table.

the below link should help you with optimization across
db links.

</code> http://www.cs.umb.edu/cs634/ora9idocs/server.920/a96544/trouble.htm#1004640 <code>

Insert slow

May 19, 2005 - 2:13 pm UTC

Reviewer: A reader

I have a fully remote query
from tab1@dblink,tab2@dblink, ...

All the tables are partitioned tables and the query just goes to 1 partition.

The SELECT returns 10 rows, is very fast.

But when I do
insert into local_table
select ...

it doesnt return even after 10 minutes.

Help? Thanks

Tom Kyte

Followup  

May 19, 2005 - 2:42 pm UTC

if you can, create a remote view that joins all of the remote tables and simply select from that (optimization takes place on remote site)

if not, this would be a candidate for going to a tiny bit of procedural code (rare, but does happen). fetch rows, insert rows.

automate,

May 20, 2005 - 10:56 am UTC

Reviewer: sns from austin,tx

We have 20 oracle instances in our warehouse environment. The management is planning to change the password of all the schemas in every database once a month.

However, we have db links in each database that points to other databases. In fact we have tens and hundereds of database links.

If the password is changed, then the db link doesn't work. We have to manually recreate the db link which is very tedious process.

Is there a way to automate this process or atleast have a stored proc that can take care of recreating the db links?

Any other ideas please?

thanks,



Tom Kyte

Followup  

May 20, 2005 - 6:28 pm UTC

centralize your user accounts -- use an ldap repository and global/enterprise users.

don't use single database accounts, use global accounts.

thanks,

May 22, 2005 - 11:50 am UTC

Reviewer: sns from austin,tx

could you please elaborate your explanation?

Is it possible to convert the existing user accounts to global users?

how to create ldap repository?

any drawbacks in using ldap repository?

thanks

Tom Kyte

Followup  

May 22, 2005 - 12:34 pm UTC

any drawbacks -- that is a rather "broad" question - unanswerable really....

But you'd want to take a look at the doc's on this (otn has them all) and if you are interested in a single book -- David Knox has a good one on security all around that covers enterprise users.


</code> http://docs.oracle.com/docs/cd/B10501_01/network.920/a96582/toc.htm <code>

is a good place to start as well.

procedure compilation with dblink leads to end-of-file communication channel.

May 23, 2005 - 5:26 am UTC

Reviewer: sreenivasa rao from INDIA

Dear Sir,

If query a table through dblink like
SQL>select * from user_roles@scmlink;
it's working fine.
And a table in size 1GB called account_master,
SQL> select * from account_master@scmlink;
this is also working .
But a procedure is using the above statement.
if i compile that procedure.then it's giving END-OF-FILE COMMUNICATION channel error.

but,I found one solution, export the target database schema and import with different schema name (1 or 2 times with different names),and recreate the DBLINK is working.since  the target DB size is 2Gb only.

unfortunatly,due to lack of transaction tracking system (save points or rollback), i need to revert the database with last export dump.At this moment the dblink creation becomes big problem.

what could be the problem?
 

Tom Kyte

Followup  

May 23, 2005 - 10:54 am UTC

please contact support for assistance with an ora-3113

Thanks TOM

May 24, 2005 - 12:39 am UTC

Reviewer: sreenivasa rao from INDIA


May 24, 2005 - 2:16 am UTC

Reviewer: alt from india

using database link is it possible to connect the same database

ie
i am using databae 'A' and i created the DB Link to the same database,when i trying to acess the table in this database using DB Link it is showing
0RA-12638 error
it will work?

Tom Kyte

Followup  

May 24, 2005 - 7:51 am UTC

depends on how you create the link, but yes you can -- I do it all of the time.

sys.link$

June 14, 2005 - 5:40 am UTC

Reviewer: Rajesh from Hyderabad, India

Tom,

Do you see any reason, why Oracle does not hash(or encrypt) the password before storing in sys.link$ table?

Even if the people who have access to sys.link$ are powerful people, they are powerful only for that database, not necessarily for the ones which are listed in sys.link$. Right?

I know, personally you are against storing plain passwords in any table. So, thought, I would give your views on this.

Thanks

Tom Kyte

Followup  

June 14, 2005 - 9:59 am UTC

because no data is stored encrypted (prior to 10gr2), and in order to store data encrypted you need to manage keys and prior to 10gr2 the database didn't have key management built into it.

the password cannot be hashed, that cannot be used to authenticate.

If you have a powerful person in that database, they do not need access to sys.link$ to use the dblinks - that is, they need not have the passwords to make use of the link. even if the password were encrypted, it would give that powerful person the same capability - just because of the existence of the dblink itself.

database link procedures and variables...

June 14, 2005 - 12:20 pm UTC

Reviewer: Phil from UK

Hi Tom

Not sure if you have already answered this so sorry if this is the same question in another format:

I have a package with some variables in the spec. I can use the package procedures and functions remotely but can I access the variables too from a dblink and if not what work-around do you recommend?



Tom Kyte

Followup  

June 14, 2005 - 4:09 pm UTC

yes, you can refer to remote packages. I find it easiest with synonyms

create synonym remote_pkg for pkg@remote;


then you can refer to remote_pkg as if it was a local one.

Oracle Object TYPEs over Database Link

July 04, 2005 - 7:58 am UTC

Reviewer: Andriy Terletskyy from Germany

Hi Tom,

how to execute(reference) a Object Type over Database link?

-- Created on 04.07.2005 by TERLETSKYY
declare
-- Local variables here
i WP.ROW_WPBWPHG9@INFO := WP.ROW_WPBWPHG9@INFO(1);
begin
-- Test statements here
i.dbms_output;
end;
/
ERROR:
PLS-00331: illegal reference to WP.ROW_WPBWPHG9@INFO.BERENBERGBANK.DE

Regards
Andriy

Tom Kyte

Followup  

July 04, 2005 - 10:44 am UTC

objects are not dblink friendly.

</code> http://docs.oracle.com/docs/cd/B10501_01/appdev.920/a96594/adobjbas.htm#466038 <code>

database links and updates

July 25, 2005 - 6:44 pm UTC

Reviewer: A reader

hi, I would like to know what happens when we update database and over the db link somebody is reading it.

OS : sun sol 8
db : oracle 8.1.7.4

issue: we have 2 indepandent databases A & B on 2 different sunboxes. both are connected via db link.
schema B1 in database B updates data based on selected data from database A, shchema A1

some thing like

start time : 00:00

execure immediate
' update B1.T1 p
set x = y
where exists (select 1 from A1.T1@db_link q
where q.c1 = p.c1 )'
;

end time : 00:15

the the problem we are facing is,
what happens if somebody
updates the data in a1.t1 ?
and issues commits

start time : 00:07
update a1.t1 q
set y =z;

commit;

end time : 00:10

q1) will new updates seen by the already running query .
q2.) what will be the sate of already running query as the later tx was commited ?
q3.) will it wait ?
q4) or query will fail ?
q5) anything other idea will also be helpful.


TIA


Tom Kyte

Followup  

July 25, 2005 - 7:45 pm UTC

... hi, I would like to know what happens when we update database and over the db
link somebody is reading it.....

same thing that happens when a database link is not involved, no different.



thanks

July 26, 2005 - 5:04 pm UTC

Reviewer: A reader

q1) will new updates seen by the already running query .
q2.) what will be the sate of already running query as the later tx was commited
?
q3.) will it wait ?
q4) or query will fail ?
q5) anything other idea will also be helpful.



Tom Kyte

Followup  

July 26, 2005 - 5:52 pm UTC

read consistency, non blocking reads.


</code> http://docs.oracle.com/docs/cd/B10501_01/server.920/a96524/c21cnsis.htm#2414 <code>

reads (the subquery) are not blocked by writes of that data.

reads (statements, or optionally the entire transaction) see a consistent view of the data.

You'll want to read that chapter.

thanks for the link.

July 27, 2005 - 2:50 pm UTC

Reviewer: A reader

thanks for the link tom.

but what I didn't get it is,
how about inserts that are committed during the query reads ?

will new commited inserts be included in the already running query result set ?

thanks,

Tom Kyte

Followup  

July 27, 2005 - 3:26 pm UTC

read consistency, most important.


The results of your query (read component) are set as of the time the query begins.


do this.


session 1 session 2
------------------ --------------------
variable x refcursor
exec open :x for select * from t;

delete from t;
commit;

print x



once you open that cursor, the result set is "fixed" as of that point in time. The results are CONSISTENT.


Same with an update, the READ component of the update is read CONSISTENT (sees data as of a single point in time)

If you have Expert One on One Oracle - I go over this in great detail

If you get the next edition volume I (coming out in Sept), I think I did it even better (the explanation and examples) 4 years later.



Or re-read that chapter above, especially:

</code> http://docs.oracle.com/docs/cd/B10501_01/server.920/a96524/c21cnsis.htm#17882 <code>



Thank you

July 27, 2005 - 3:29 pm UTC

Reviewer: A reader

thanks, for showin me "How to Test", this is real good
now I will actually know what I am testing...

thanks

dynamically recreating db links,

August 13, 2005 - 5:05 pm UTC

Reviewer: sns from austin,tx

On Linux platform we have a file that stores the name of the database, the schema name and its password (delimited by ":" )
Every month the passwords across all the databases changes and the configuration management person updates the file with the new password.

The issue with us is the db links needs to be recreated. A schema of some database may have db links to all other databases.

In simple words, there are 100's of db links.

We need to change them all right after the file gets updated with the new password.

Given this scenario, what would be your steps to recreate db links? Do you use the combination of shell script and pl/sql or just pl/sql or even just shell script?

Could you share the script if you have already written one?

Thanks,

Tom Kyte

Followup  

August 13, 2005 - 5:50 pm UTC

wow, why bother with passwords if you are going to store them in a file like that?

Sounds like you need a centralized repository, a directory of sorts, a central place to manage and maintain this information. Perhaps even the introduction of PKI so as to not use passwords at all.

We use LDAP for this, our implementation is OID (Oracle Internet Directory). There are others on the market as well.

password,

August 14, 2005 - 9:31 am UTC

Reviewer: sns from austin,tx

The file is secured and only certain people can view the password. We have a shell script that takes two parameters: DB name and Schema name and it returns password back.

The shell script checks who has execute privilege to execute the getpassword file.

This idea is perhaps some people who have pretty minimum knowledge on oracle features. Our warehouse shop is mainly in Teradata and few of them are oracle marts.

Anyway, implementing LDAP is pretty far away for us.

Thanks,

Tom Kyte

Followup  

August 14, 2005 - 9:36 am UTC

The file is secured and only certain people can view the password.

uh huh.


Well, no scripts from me. I don't have anything remotely similar.

Performance over dblinks

August 25, 2005 - 12:51 pm UTC

Reviewer: Chris from Louisville, KY

Tom,
I am working to get some specifics for you, but in the meantime I thought I'd ask the question and you may point me in a direction to look. Our production database uses a database link to look data up on a remote database. In general (probably 99.9% of the time) the query and response comes back very quickly (0 - 250 milliseconds). However, the other 0.1% of the time it takes 5 - 8 seconds. Does that ring any bells with you. I'm going over to work with the team to get the code and see if it can be reproduced and will update if I can. Just thought you might have some ideas or areas I should focus on.

Tom Kyte

Followup  

August 25, 2005 - 6:31 pm UTC

My gut says "network burp, long dns lookup" or "remote server really smashed at that time, connect takes very long"

but, a sql_trace would help if possible (10046 level 12 with waits)

Performance over DB link

August 29, 2005 - 12:07 pm UTC

Reviewer: HR

I have the query, all the objects in DB1.
it runs 1 second direct on DB1, and it runs over one minute over the db link on DB2. it always runs over one minute on DB2. The query only returns 20 records, so i do not think because of data size returned is the problem.

I tested another query which has very small table in DB1,
and it runs as much as the same time on DB1 or via db link on DB2.

How can i look?

TIA

Tom Kyte

Followup  

August 29, 2005 - 1:57 pm UTC

look at the plans, you might use the driving_site hint to have it optimized on db1 when run from db2

Perf over Db link

August 29, 2005 - 3:00 pm UTC

Reviewer: HR

Thanks tom.
the query from the DB2 via db link:
SELECT
DECODE(f.phase_code,'C', 'Completion', 'P', 'Pending', 'R', 'Running') status_code,
f.request_id,
u.user_name||': '||substr(u.description,1, instr(u.description, '(' )-1 ) user_name,
TRUNC(((sysdate - f.actual_start_date)/(1/24))*60) runtime,
DECODE(u.user_name, 'U4IC9GAN', 'Scheduled', 'U4ICAADW', 'Scheduled','SYSADMIN', 'Scheduled',
DECODE(f.phase_code, 'R', TRUNC(((f.actual_start_date - f.REQUEST_DATE)/(1/24))*60),
'P', TRUNC(((sysdate - f.REQUEST_DATE)/(1/24))*60) ) ) waittime,
avg(DECODE(u.user_name, 'U4IC9GAN', 0, 'U4ICAADW', 0, 'SYSADMIN', 0,
DECODE(f.phase_code, 'R', TRUNC(((f.actual_start_date - f.REQUEST_DATE)/(1/24))*60),
'P', TRUNC(((sysdate - f.REQUEST_DATE)/(1/24))*60) ))) over () avg_wait,
f.actual_start_date asd,
f.REQUEST_DATE reqtime,
DECODE(p.concurrent_program_name, 'ALECDC', p.concurrent_program_name||'['||f.description||']',
p.concurrent_program_name) cpn,
DECODE(s.ARGUMENT_TEXT , '(None)', 'USACE', null, 'HOSTNATION', s.ARGUMENT_TEXT) parameters
FROM apps.fnd_concurrent_programs@oracle_projects p,
apps.fnd_concurrent_programs_tl@oracle_projects pt,
apps.fnd_concurrent_requests@oracle_projects f,
apps.fnd_user@oracle_projects u,
apps. fnd_conc_req_summary_v@oracle_projects s
WHERE
f.concurrent_program_id = p.concurrent_program_id
and f.phase_code in ('P', 'R')
AND f.program_application_id = p.application_id
AND f.concurrent_program_id = pt.concurrent_program_id
AND f.program_application_id = pt.application_id
AND f.requested_by = u.user_id
AND pt.language = USERENV('Lang')
and s.request_id= f.request_id
and DECODE(p.concurrent_program_name, 'ALECDC', p.concurrent_program_name||'['||f.description||']',
p.concurrent_program_name) like 'OP3%'
ORDER BY runtime, waittime desc
/

the plan on DB2:
QUERY_PLAN
-----------------------------------------
WINDOW SORT
HASH JOIN
NESTED LOOPS
HASH JOIN
NESTED LOOPS
REMOTE
FILTER
REMOTE
REMOTE
REMOTE
REMOTE
---
The plan on DB1:
QUERY_PLAN
------------------------------------------------------------
WINDOW SORT
NESTED LOOPS
NESTED LOOPS
NESTED LOOPS
NESTED LOOPS OUTER
NESTED LOOPS
NESTED LOOPS
NESTED LOOPS
NESTED LOOPS
INLIST ITERATOR
TABLE ACCESS BY INDEX ROWID FND_CONCURRENT_REQUESTS

INDEX RANGE SCAN FND_CONCURRENT_REQUESTS_N7

INDEX UNIQUE SCAN FND_CONCURRENT_PROGRAMS_TL_U1

TABLE ACCESS BY INDEX ROWID FND_CONCURRENT_PROGRAMS

INDEX UNIQUE SCAN FND_CONCURRENT_PROGRAMS_U1

TABLE ACCESS BY INDEX ROWID FND_USER
INDEX UNIQUE SCAN FND_USER_U1
TABLE ACCESS BY INDEX ROWID FND_CONCURRENT_REQUESTS

INDEX UNIQUE SCAN FND_CONCURRENT_REQUESTS_U1
INDEX UNIQUE SCAN FND_PRINTER_STYLES_TL_U1
INDEX UNIQUE SCAN FND_CONCURRENT_PROGRAMS_U1
INDEX UNIQUE SCAN FND_CONCURRENT_PROGRAMS_TL_U1
INDEX UNIQUE SCAN FND_USER_U1

looks like the driving_site may not apply here, the query runs and optmized on DB1?


Tom Kyte

Followup  

August 30, 2005 - 12:53 am UTC

the driving site hint would let you tell db1 to optimize the query in db2, that was the point.

Using DBLINK between Oracle and MS SQL Server

September 07, 2005 - 2:57 am UTC

Reviewer: acaicb from CN

Hi,Tom.
Somebody told me that a connection can be created between Oracle DB and MS SQL Server using DB LINK.
Is it right?
if it is right,how I use DB LINK to create a connection?

Tom Kyte

Followup  

September 07, 2005 - 7:51 am UTC

</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:4406709207206#18830681837358 <code>

use odbc

View with CLOB column to hide link?

September 28, 2005 - 9:16 pm UTC

Reviewer: Vernon from California, USA

Tom,

You said that you like to use views to conceal the link and provide a local copy of the metadata. Is there any way to do this when the remote table contains a CLOB column?

I only want to be able to push data to the remote table with a package using insert into x@y (...) select ... from local_y

If the remote database is unreachable, any attempt to recompile the package body causes my session to hang until connectivity is returned.

Thanks

Tom Kyte

Followup  

September 29, 2005 - 6:42 am UTC

In this case, you can use native dynamic sql to work around this issue. That'll break the dependency between the procedure and the dblink as well.

In general I'd be opposed to this however, in versions prior to 10g, native dynamic sql causes a parse per execute, you lose the dependency, it is not as efficient.



A Reader

September 29, 2005 - 5:33 am UTC

Reviewer: A from Aus

Hi,
Is there any way/trick to hide password from getting display/stored in user_db_link.I have a transactional system
and report system(on different box) .Report system should have read only rights on production(trans) system .I was thinking to create db link ,but the password is a problem(gets stored in user_db_links) which I don't want.Any way to hide this.

Cheers

Tom Kyte

Followup  

September 29, 2005 - 7:09 am UTC

can it be a public database link?

you can put it into another schema and create views there and grant on the views to this first schema (so someone else owns it)

performance related issue using db links,

October 03, 2005 - 2:10 pm UTC

Reviewer: sns from austin,tx

I have a query with joins on two different tables that runs in under 2 minutes.  However, when I run the same query from other database accessing the objects using db link, it is taking almost 15 times.

Here are the details:

SQL> connect user@dbname1
Enter password: 
Connected.
SQL>  select count(*) from (
  2   select distinct d.order_num, d.tie_num, d.sku_num, d.mfg_part_num, d.order_qty, d.item_class, d.system_class
  3   from lata.prod_order_detail_lata_usd d, lata.prod_order_summary_lata_usd s
  4   where s.business_unit_id <> 2020
  5   and (s.order_date >= sysdate - 8
  6   or        s.status_date >= sysdate - 8
  7   or        s.order_status in ('IP', 'PP', 'HL', 'TR'))
  8   and s.order_num = d.order_num
  9   and d.mfg_part_num is not null
 10   )
 11  ;

  COUNT(*)
----------
    425341
Elapsed: 00:01:36.94

Running using a DB_LINK:

connect user@dbname2
Enter password: 
Connected.
SQL> select count(*) from (
  2  select distinct d.order_num, d.tie_num, d.sku_num, d.mfg_part_num, d.order_qty, d.item_class, d.system_class
  3  from lata.prod_order_detail_lata_usd@dblink.world d, lata.prod_order_summary_lata_usd@dblink.world s         
  4  where s.business_unit_id <> 2020
  5  and (s.order_date >= sysdate - 8
  6  or        s.status_date >= sysdate - 8
  7  or        s.order_status in ('IP', 'PP', 'HL', 'TR'))
  8  and s.order_num = d.order_num
  9  and d.mfg_part_num is not null);

  COUNT(*)
----------
    425341
Elapsed: 00:33:53.33

How do you trouble shoot this kind of issue?  What are the things you look into for analyzing the drastic time difference.

I know accessing through db link is slower but I didn't expect this much.

Thanks, 

Tom Kyte

Followup  

October 03, 2005 - 8:55 pm UTC

first thing, get the plans and compare them...


you are using the CBO with stats and all right?

remote query limitations

October 18, 2005 - 12:17 pm UTC

Reviewer: A reader

Hi

I have a select count(*) query which runs very fast in local but slow from a remote server (database link)

I noticed the local query uses this execution plan

BITMAP CONVERSION* (COUNT)
BITMAP INDEX* (FULL SCAN) OF 'I_SUME_ESTADO

However the remote query runs a full table scan

Is this a database link limitation?

Tom Kyte

Followup  

October 18, 2005 - 2:21 pm UTC

could be - but have you tried the driving site hint out?

November 21, 2005 - 2:50 pm UTC

Reviewer: A reader


create DB link under other schema name

November 30, 2005 - 5:58 pm UTC

Reviewer: A reader from US

Tom,

Is there a way to create a db link under other schema names?
As user "sys", how to create a private db link under schema "hr"? it does not work the same way as other objects

thanks,


Tom Kyte

Followup  

November 30, 2005 - 9:05 pm UTC

not that am am aware of.

can I come up with a way to do it - yes.... it would involve having some DBA account (because we all know not to use sys for stuff). it would not be "pretty" or "elegant".

of course you can always use "su"
</code> http://asktom.oracle.com/Misc/su.html <code>

create DB link under other schema name - ctd

December 01, 2005 - 4:03 am UTC

Reviewer: Serge Shmygelsky from Ukraine

Why can't we use ALTER SESSION SET CURRENT_SCHEMA=<owner>? I made a simple test:

SYS@REX> conn shmyg as sysdba;
Enter password: ********
Connected.
SYS@REX> alter session set current_schema=dealer;
SYS@REX> create table test (f1 number);
SYS@REX> select * from all_tables where table_name = 'TEST';

OWNER TABLE_NAME
------------------------------ ------------------------------
DEALER TEST
SYS@REX> create database link bscs connect to scott identified by tiger using 'test6';
create database link bscs connect to scott identified by tiger using 'test6'
*
ERROR at line 1:
ORA-01031: insufficient privileges

SYS@REX> conn dealer/dealer
Connected.
DEALER@REX> create database link bscs connect to scott identified by tiger using 'test6';
DEALER@REX>

Why can we create a table and not database link?

Tom Kyte

Followup  

December 01, 2005 - 12:35 pm UTC

never use sysdba for stuff, never - use it to startup and shutdown. don't use it day to day.

sysdba (sys) is special, magical, different. do not use it. use it to maybe create your first account and then stop using it.


set current schema does not change anything privilege wise, it simply changes the current default schema name that would be coded into the sql statement.


select * from t

becomes as if you had typed in:

select * from CURRRENT_SCHEMA.t

if, you could not select * from current_schema.t before the alter, you cannot after, it changes nothing about the privilege domain.

create DB link under other schema name - ctd

December 02, 2005 - 5:13 am UTC

Reviewer: Serge Shmygelsky from Ukraine

Hello Tom,

yes, I know what ALTER SESSION SET CURRENT_SCHEMA is doing. I was just wondering why it is possible to create a table in the schema we switched to and not a database link.

P.S. You've already taught me not to use SYS account :). It was just a copy-paste after starting up the database which I cut off :)

Thanks in advance for your response.

Tom Kyte

Followup  

December 02, 2005 - 10:56 am UTC

because private database links do not support "schemas".


</code> http://docs.oracle.com/docs/cd/B19306_01/server.102/b14200/statements_5005.htm#sthref4974 <code>

the syntax, unlike create table for example, doesn't have the concept of a schema name associated with it.

executing remote db package using db link and synonym

December 20, 2005 - 12:00 pm UTC

Reviewer: Kuldeep from India

Dear Tom,

My requirement is to make available a remote package to my local database. Remote package contains around 30 procedure and functions. so I cant make 30 synonym for each procedure and function of package.

I searched your site. now I am able to call remote package's procedure easly but in the case of calling remote package's function I am facing error.

steps what i followed:

sql> create database link mylink connect to RUSER identified by RPWD using 'RCSTR';

sql> desc rpkg@mylink
procedure p1
function f1 return number

sql> create synonym RSYN for rpkg@mylink;

sql> set serveroutput on

sql> exec rsyn.p1
PL/SQL procedure successfully completed.

sql> select rsyn.f1 from dual;
select rsyn.f1 from dual
       *
ERROR at line 1:
ORA-00904: "rsyn"."f1": invalid identifier

while

SQL> declare 
  2  a number;
  3  begin
  4  a:=rsyn.f1;
  5  dbms_output.put_line(a);
  6  end;
  7  /
75

PL/SQL procedure successfully completed.

How can I call remote package's functions in my SQLs.

Thanks and regards, 

Tom Kyte

Followup  

December 20, 2005 - 1:01 pm UTC

why is "rsyn"."f1" in "lower" case ?

should be "upper" case:

ops$tkyte@ORA10GR2> select a.b from dual;
select a.b from dual
       *
ERROR at line 1:
ORA-00904: "A"."B": invalid identifier


 

Strange

December 22, 2005 - 7:46 pm UTC

Reviewer: abc

Tom

I dont have any db link which is pointing to REP server but when I do 
SQL>  select  count(1)   from mgr_fpa.region_ref@rep;
 select  count(1)   from mgr_fpa.region_ref@rep
                                            *
ERROR at line 1:
ORA-28000: the account is locked
ORA-02063: preceding line from REP

REP is db link going to REPU

SQL> select *   from dba_objects where object_name like '%rep%';

OWNER                          OBJECT_NAME                                                                                                                      SUBOBJECT_NAME
------------------------------ -------------------------------------------------------------------------------------------------------------------------------- ------------------------------
 OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE        CREATED         LAST_DDL_TIME   TIMESTAMP           STATUS  T G S
---------- -------------- ------------------ --------------- --------------- ------------------- ------- - - -
SYS                            /3e096b67_OraclePreparedStatem
    122963                JAVA CLASS         24-JUN-01       15-FEB-04       2002-03-02:10:03:45 VALID   N N N

SYS                            /4784edfa_OraclePreparedStatem
    122961                JAVA CLASS         24-JUN-01       15-FEB-04       2002-03-02:10:03:45 VALID   N N N

SYS                            /8af1ab71_coreproperties
    132586                JAVA RESOURCE      24-JUN-01       02-MAR-02       2002-03-02:09:57:08 VALID   N N N

SYS                            /b267ff29_OraclePreparedStatem
    122965                JAVA CLASS         24-JUN-01       15-FEB-04       2002-03-02:10:03:45 VALID   N N N

SYS                            /bf824cc6_RTStatementJDBCPrepa
    121825                JAVA CLASS         24-JUN-01       15-FEB-04       2002-03-02:10:04:17 VALID   N N N

SYS                            java/sql/PreparedStatement
    125165                JAVA CLASS         24-JUN-01       15-FEB-04       2002-03-02:10:03:06 VALID   N N N

PUBLIC                         /18d4f450_MAnnSQLPreprocessorS
   5499446                SYNONYM            16-FEB-04       16-FEB-04       2004-02-16:00:52:49 VALID   N N N

PUBLIC                         /3e096b67_OraclePreparedStatem
    122964                SYNONYM            15-FEB-04       15-FEB-04       2004-02-15:20:52:02 VALID   N N N

PUBLIC                         /4784edfa_OraclePreparedStatem
    122962                SYNONYM            15-FEB-04       15-FEB-04       2004-02-15:20:51:59 VALID   N N N

PUBLIC                         /975e31e9_MAnnSQLPreprocessorV
   5499448                SYNONYM            16-FEB-04       16-FEB-04       2004-02-16:00:52:49 VALID   N N N

PUBLIC                         /b267ff29_OraclePreparedStatem
    122966                SYNONYM            15-FEB-04       15-FEB-04       2004-02-15:20:52:03 VALID   N N N

PUBLIC                         /ba6941e2_MAnnSQLPreprocessor
   5499449                SYNONYM            16-FEB-04       16-FEB-04       2004-02-16:00:52:49 VALID   N N N

PUBLIC                         /bd14c239_MAnnSQLPreprocessorE
   5499445                SYNONYM            16-FEB-04       16-FEB-04       2004-02-16:00:52:49 VALID   N N N

PUBLIC                         /bf824cc6_RTStatementJDBCPrepa
    121826                SYNONYM            15-FEB-04       15-FEB-04       2004-02-15:20:47:04 VALID   N N N

PUBLIC                         /efef3908_MAnnSQLPreprocessorS
   5499447                SYNONYM            16-FEB-04       16-FEB-04       2004-02-16:00:52:49 VALID   N N N

PUBLIC                         java/sql/PreparedStatement
    125166                SYNONYM            15-FEB-04       15-FEB-04       2004-02-15:20:52:11 VALID   N N N

ORDSYS                         /18d4f450_MAnnSQLPreprocessorS
     21085                JAVA CLASS         01-MAY-00       16-FEB-04       2004-02-16:00:52:04 VALID   N N N

ORDSYS                         /975e31e9_MAnnSQLPreprocessorV
     21087                JAVA CLASS         01-MAY-00       16-FEB-04       2004-02-16:00:52:04 VALID   N N N

ORDSYS                         /ba6941e2_MAnnSQLPreprocessor
     21088                JAVA CLASS         01-MAY-00       16-FEB-04       2004-02-16:00:52:04 VALID   N N N

ORDSYS                         /bd14c239_MAnnSQLPreprocessorE
     21084                JAVA CLASS         01-MAY-00       16-FEB-04       2004-02-16:00:52:04 VALID   N N N

ORDSYS                         /efef3908_MAnnSQLPreprocessorS
     21086                JAVA CLASS         01-MAY-00       16-FEB-04       2004-02-16:00:52:04 VALID   N N N



Please suggest 

Tom Kyte

Followup  

December 22, 2005 - 8:36 pm UTC

unlock the account?

executing remote db package using db link and synonym

December 28, 2005 - 11:57 am UTC

Reviewer: kuldeep from India

Dear Tom,

Thanks for your response.

In my last post the lower case identifier was because I edited the names of the identifiers. Sorry I typed in lower case. But the rest of the things were correct.

There is another example (copy and past as it is)
---------------
SQL> 
SQL> desc pkgp1
FUNCTION F RETURNS NUMBER
PROCEDURE P

SQL> exec pkgp1.p

PL/SQL procedure successfully completed.

SQL> select pkgp1.f from dual;
select pkgp1.f from dual
       *
ERROR at line 1:
ORA-00904: "PKGP1"."F": invalid identifier


SQL> 
---------------

Thanks and regards, 

Tom Kyte

Followup  

December 28, 2005 - 5:40 pm UTC

I have tested on 10gR2 and cannot reproduce.

Versions involved here?

strange

December 28, 2005 - 1:46 pm UTC

Reviewer: abc

Unlock is fine but myh concern is there is no dblink poinitng to prodocution REP then why this connection login to REP

I dont have any db link which is pointing to REP server but when I do 

what are the following objects?
SQL>  select  count(1)   from mgr_fpa.region_ref@rep;
 select  count(1)   from mgr_fpa.region_ref@rep
                                            *
ERROR at line 1:
ORA-28000: the account is locked
ORA-02063: preceding line from REP

REP is db link going to REPU

SQL> select *   from dba_objects where object_name like '%rep%';

OWNER                          OBJECT_NAME                                       
                                                                               
SUBOBJECT_NAME
------------------------------ 
---------------------------------------------------------------------------------
----------------------------------------------- ------------------------------
 OBJECT_ID DATA_OBJECT_ID OBJECT_TYPE        CREATED         LAST_DDL_TIME   
TIMESTAMP           STATUS  T G S
---------- -------------- ------------------ --------------- --------------- 
------------------- ------- - - -
SYS                            /3e096b67_OraclePreparedStatem
    122963                JAVA CLASS         24-JUN-01       15-FEB-04       
2002-03-02:10:03:45 VALID   N N N

SYS                            /4784edfa_OraclePreparedStatem
    122961                JAVA CLASS         24-JUN-01       15-FEB-04       
2002-03-02:10:03:45 VALID   N N N

SYS                            /8af1ab71_coreproperties
    132586                JAVA RESOURCE      24-JUN-01       02-MAR-02       
2002-03-02:09:57:08 VALID   N N N

SYS                            /b267ff29_OraclePreparedStatem
    122965                JAVA CLASS         24-JUN-01       15-FEB-04       
2002-03-02:10:03:45 VALID   N N N
 

Tom Kyte

Followup  

December 28, 2005 - 5:54 pm UTC

object names, unless quoted, are stored in upper case.

it would be %REP%, not %rep%


and you do not necessarily need to have a database link created with global names and the proper setup, the database will use the current credentials and connect to the remote database using them.

strange

December 28, 2005 - 6:58 pm UTC

Reviewer: abc

Tom,

Do you think it makes any sense?

Select * from dual@rep from repu is giving invalid password and causing failed login attempts in REP because of Tns enteries .
We are using ONAMES.
There is no db link pointing to production server REP

Tom Kyte

Followup  

December 28, 2005 - 8:13 pm UTC

yes.

executing remote db package using db link and synonym

January 03, 2006 - 8:37 am UTC

Reviewer: Kuldeep from India

Dear Tom,

Thanks again for your response.

I am using Oracle 9.2.0.1.0 on Windows2000.

Regards,

Tom Kyte

Followup  

January 03, 2006 - 8:43 am UTC

I'll have you work with support - but they'll probably ask you to apply the current patchset to get the 4th digit relatively up to date in your version.

With reference to earlier post in thread

January 03, 2006 - 12:10 pm UTC

Reviewer: Matt from UK

In a review to this thread above:
</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:456820211101#38461801491167 <code>

There is a suggestion that it is possible to create a database link to an MS access database. Is this indeed possible?

I'm looking to obtain a connection to an MS ACCESS database from Oracle 9.2.0.6 to carry out some ad-hoc querying and reporting. I have briefly looked at Heterogeneous services, which look to be a little like overkill for what I am trying to achieve. I am really just looking for a "quick and dirty" connection to carry out some queries/reporting from Oracle.

Do you have a link to the doco that explains how to configure Net services to allow a connection to a non-oracle DB such as MS ACCESS?

P.S Looking forward to the asktom re-write. Finally a real WAP interface :o)

Many thanks in advance.

Regards,


Tom Kyte

Followup  

January 03, 2006 - 12:51 pm UTC

yes:
</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:4406709207206#18830681837358 <code>

ODBC in general... Heterogenous services are the way to do this.

Can we execute DDL's using Database links

January 10, 2006 - 11:53 am UTC

Reviewer: Matte from Austin,Tx

Is it possible to execute create/alter/drop statements on remote database by using database link?


Tom Kyte

Followup  

January 10, 2006 - 1:09 pm UTC

you cannot do ddl over a database link.

db links and security

January 11, 2006 - 6:13 pm UTC

Reviewer: sudershan from usa

oracle 9.2.0.6
Tom,
In case of private database links..besides user_db_links..
is there any other place where text password is visible.


Tom Kyte

Followup  

January 12, 2006 - 10:53 am UTC

sys.link$

DBLink with Analytic Function

January 13, 2006 - 4:58 am UTC

Reviewer: Joe from Malaysia

Hi Tom,

I have a case here where a dblink is used to insert some records from the local DB to the remote DB.

The statement looks something like this:


INSERT INTO TARGET_TABLE@DBLINK
SELECT SOURCE.*
FROM SOURCETABLE SOURCE
WHERE LOG_ID IN
(
SELECT LOG_ID
FROM (
SELECT
LOG_ID,
MAX(LOG_DATE) OVER (PARTITION BY LOG_GRP_ID) AS MAXDATE
FROM LOG_HIST
WHERE
TRUNC(LOG_DATE) >= TO_DATE('03-AUG-2005','DD-MON-YYYY')- 1
AND TRUNC(LOG_DATE) <= TO_DATE('09-DEC-2005','DD-MON-YYYY')
AND audit_log_table = 'SOMETABLE'
) TBLA
WHERE TRUNC(TBLA.MAXDATE) >= TO_DATE('03-AUG-2005','DD-MON-YYYY')
AND TRUNC(TBLA.MAXDATE) < TO_DATE('09-DEC-2005','DD-MON-YYYY')
AND TBLA.LOG_ID = SOURCE.LOG_ID
);


Total records selected and inserted is around 200 records only.

The statement runs for > 2 minutes. But when i remove the INSERT INTO part,the SELECT itself runs in < 1 second.

Upon further investigation when I :

1. remove the DBLINK and insert into a local table, the statement completes in < 1 second.
2. remove the OVER PARTITION BY but still use DBLINK, the statement also completes in < 1 second.

So I figure it is a problem when analytic functions are used in combination with DBLink.

Currently the temporary workaround is to INSERT into a local table first along with the OVER PARTITION BY.
Then SELECT from the local table to the DBLINK table.
This takes around 1-2 seconds.

I am still trying to figure out why the DBLINK and OVER PARTITION BY combination results in such poor performance.
Is there an explanation why this is so? Is there a problem with Oracle when using analytic functions such as OVER PARTITION BY with DBLINK.



Preferred method to grant access to linked objects

January 16, 2006 - 6:02 pm UTC

Reviewer: Sudershan from USA

Oracle 9.2.0.6.0
Hi Tom,
What is your preferred link method to give access to users
for remote objects.
I use a one user that own the links (with the password)..and
that user then grant access to other users..this way no one else has access to the link.
Password is visible only to the schema that owns the link..
and through sys.link$ (so make sure no one has access to this sys table).
What do you think about this approach in terms of security?

Thanks.


Tom Kyte

Followup  

January 16, 2006 - 9:02 pm UTC

depends entirely on your NEEDS.

what you've set up is a proxy database link, all users will be "proxied" into the other database using that individuals credentials. If that is what you need - that is what you need.

Else, you would create the database link without a username/password and let the current users credentials be used. If that is what you need.

January 23, 2006 - 11:18 am UTC

Reviewer: virgile CREVON from france

Hi,
Why not using DB_LINKs with embedded CONNECT_STRING ??
Many of the questions here would have been solve with this kind of trick.

Here's an example :

scott@8i> create database link ora8idev
2 connect to scott
3 identified by tiger
4 using 'ora8idev'
5 /

use this instead :

scott@8i> create database link ora8idev
2 connect to scott
3 identified by tiger
4 using '(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS =
(PROTOCOL = TCP)
(HOST = MYHOSTHERE)
(PORT = MYPORTHERE)
)
)
(CONNECT_DATA =
(SID = MYSIDHERE)
)
)'
5 /

Pro : only user with db_link can modify the DB_LINK definition (without this trick, anybody can modify TNSNAMES.ORA and, suddenly, the app stop responding ...).
Con : always the password stored in CLEAR...

Regards,

Virgile



Tom Kyte

Followup  

January 23, 2006 - 11:50 am UTC

the con has nothing to do with the question though - they both have that attribute, it is not any different.


You can use either construct, it is up to you.

Also getting ORA-02019

January 30, 2006 - 1:52 pm UTC

Reviewer: V from East coast

Here is the setup, on Oracle 9.2.0.6, Windows 2003

SQL> connect SchemaA/password@NSN1

SQL> create database link MyLink1
2 connect to VCG identified okm135
3 using 'STAF'
4 /

Database link created.

SQL> create or replace VIEW rem_mydocs as
2 (select * from mydocs@MyLink1)
3 /

View created.

SQL> grant select on rem_mydocs to UserA ;

Grant succeeded

SQL> Create or replace function fn_rem_mydocs 
2 return Sys_RefCursor 
3 IS
4 v_rc Sys_RefCursor;
5 begin
6  open v_rc for 
7       select * from rem_mydocs ;
8  return (v_rc);
9 end;
10 /

Function created.

SQL> grant execute on fn_rem_mydocs to UserA;

Grant succeeded

SQL> connect UserA/test975@NSN1
Connected.

SQL> create or replace synonym rem_mydocs for SchemaA.rem_mydocs;

Synonym created.

SQL> create or replace synonym fn_rem_mydocs for SchemaA.sp_rem_mydocs ;

Synonym created.

SQL> select count(*) from rem_mydocs ;

 COUNT(*)
---------
      324

SQL> var g_ref refcursor
SQL> begin :g_ref := fn_rem_mydocs; end;
2 /

SQL> print g_ref
ERROR:
ORA-02019: connection description for remote database not found

I have not been able to figure it out.  Any help would be greatly appreciated.
 

Tom Kyte

Followup  

January 30, 2006 - 3:43 pm UTC

I'll have to ask you to work with support on this one, nothing pops immediately to mind.

Also getting ORA-02019

February 02, 2006 - 10:59 am UTC

Reviewer: V from East Coast

Although there was an Bug reported for this error, the symptom where different. So, I kept looking for a solution and found a workaround to my problem. Invoker Rights

I created the function with AUTHID CURRENT_USER
and now it works.

create or replace function fn_rem_mydocsreturn Sys_RefCursor

AUTHID CURRENT_USER

is
v_rc Sys_RefCursor;
begin
open v_rc for select * from rem_mydocs ;
return (v_rc);
end;
/



Tom Kyte

Followup  

February 02, 2006 - 12:15 pm UTC

that completely changes the behavior of this entirely - you do understand that right. entirely and compleletly changes the behavior

this workaround is really "we've changed what we want from the database"

Refcursor over database link

February 09, 2006 - 11:16 am UTC

Reviewer: William from Europe

Hi Tom,

Is it possible in 9iR2 to use a refcursor over a database link?

As follows:
DB1
function get_attributes (p_type in varchar2
, p_date in date
)
return sys_refcursor
is
result sys_refcursor;
begin
execute immediate 'alter session set hash_join_enabled = true';

open result for
select PRDID
, NAME
, DATATYPE
, STRINGVALUE
, FILENAME
from fe_lpd_attributevalue
where ( date_inserted > p_date
or date_modified > p_date
)
and ( SECOND_PRD_TYPE = p_type
or ( p_type is null and SECOND_PRD_TYPE <> 'B')
);
--
return result;
end;

DB2
procedure grab ( p_type in varchar2 default null) is
c sys_refcursor;

l_number number;
l_value2 varchar2(200);
l_value3 varchar2(200);
l_value4 varchar2(200);
l_value5 varchar2(2000);
l_value6 varchar2(200);
l_value7 varchar2(200);
l_value8 varchar2(200);
l_value9 varchar2(200);

begin
-- this function is a remote call on another DB!!!
c := GET_ATTRIBUTES(p_type ,sysdate);

fetch c into l_number
, l_value3
, l_value4
, l_value5
, l_value6
;

close c;

end if;

end grab;




When I run the procedure Grab on DB2 i am getting an error:

ERROR at line 1:
ORA-01007: variable not in select list

for the moment i cannot find out what happens so I just want to know if it is possible to use a refcursor over a database link?

Kind regards,

William

Tom Kyte

Followup  

February 10, 2006 - 11:17 am UTC

refcursors may not be returned over a dblink:

</code> http://docs.oracle.com/docs/cd/B19306_01/appdev.102/b14261/sqloperations.htm#sthref1448 <code>

that is what the somewhat obscure wording:

...
Using a REF CURSOR variable in a server-to-server RPC results in an error. However, a REF CURSOR variable is permitted in a server-to-server RPC if the remote database is a non-Oracle database accessed through a Procedural Gateway.
......

is meant to convey. It could be said a bit more clearly probably. You are trying to do a "server to server RPC"

performance issues which is better

February 13, 2006 - 5:11 am UTC

Reviewer: daniel from KSA

Hi Tom,
We have a database that is very heavy oltp and we have around 300 tran/sec with a redo size of 1,727,818 per sec.
The top 50 to 60% wait in the top5 wait event is log_file_sync.
We tried to fix the io and other things, but we could not reduce much waits and now it seems that we have to batch the commits but thats design change and nature of application is not allowing this. We have the following idea:
We know that out of 300 tran per sec, around 60% of the commits come from one process(price-engine) which keeps on updating 2 tables which have share price of each production that application sells.
Now we are thinkign of:

1. Creating another instance(InsB) and in that instance copying the above 2 tables. The Price-Engine will now update the InstanceB and not InstanceA.
But note that users (500) will connect to the first db as before.
2. The first instanceA wil also have these 2 tables, but we will create a unix-java process which will have one connections to each of these databases.
What this process will do is to read the two tables continusoly every 1/2 sec from instanceB, and will send updates to the first InstanceA and then commits.

Note that the price-engine will update the two tables in InstanceB heavily say like 100 updates in 1 sec , but we only replicate at every 1/2 sec to the first instance, which is acceptable to our business users.

This way we reduce the load on instance A.

Now the question is " is there a better way"
We dbas suggested that we do not neeed to have the tables in the first instance, we wil create synoms in dblink over the two instance and 500 users will read the 2 tables online on the seond db via db link.
bUT this way every time there will be a connection created on second instance.

Is there a connection pooling or something in dblink that will make dblink to remain connect all the time???
cheers





Tom Kyte

Followup  

February 13, 2006 - 8:35 am UTC

but how big are the waits. you will always and forever have a top 5 timed events.

And if the price engine (sounds like a background process) is the biggest waiter for this - what effect will this have on the end users - will it change them at all.

eg: go to an application level trace, show yourself that the end users are waiting massively on this - before touching a thing.


logfile sync

February 15, 2006 - 12:49 am UTC

Reviewer: daniel from ksa

Hi Tom.

The top wait is the logfile sync wait which was 60% last week.
If you recall i asked a question some time back about logfile sync waits and you told me that to do that i have to batch COMMITS or increase speed of my san which is ibm es800-shark.

Now the good news is that yesterday we solved this problem.
(the problem was not solved when i wrote this thread).

I have a tar opebed for this for 1 month and all oracle engineers can do was the same reply as you said.

Anyway what i did was asked the aix admin to create me a separate mount point on same san say '/redolog' but mount it with cio(concur io) option, this is like having a raw device but with a file system(aix 5.3 and oracle metalink note suggests that;docid:245356.1
And the logfile waits are gone, they are now 3% as compared to 60%. And out users have conformed that app is now performing efficiently, and our price engines etc have not more thruput i.e. we increased no of tran/sec.

My advise to that metalink engineer was:
Try having some expertise in oracle support from os point of view. if they could only ask us to put a trace of logwr , perhaps some one in oracle who knows the os basics can tell us where we are having issues.

Anyway the effect of cio mount point (bypassing the os cache0 is exponential.

We are so happy that we achieved this.

You may term this as not an oracle problem in the first place, yes i agree but i wish if there are multi role experts in oracle support. All they do is to first try to force you to upgrade to latestt patch and then if not solve, contact your os vendor. I mean this is so unacceptable from management point of view, we do not want to be in between oracle and ibm pointing fingers.

Cheers














Tom Kyte

Followup  

February 15, 2006 - 9:10 am UTC

... increase speed of my san
which is ibm es800-shark. ...

which is precisely what you did. You cannot expect us to know your hardware and be able to tell you how to make your hardware better? I mean, maybe you do - but it isn't going to be a reasonable request.

You made your log device faster, many articles on this site suggest using forcedirectio (an option on Solaris) - not knowing your hardware (we don't all have your configuration) makes it, well, sort of difficult.


Performance using dblink and join operations.

February 20, 2006 - 5:15 am UTC

Reviewer: Jorge from Madrid, Spain

Hi Tom!,

We have two separate databases on different machines. The question is very simple. What should I consider (about performance) if I do a join between a local instance with another remote instance?. Suppose I have an instance A and another remote B. My query is select * from a A,b@dblink B where A.x=B.y. Is it true that remote data from B is sent to the data buffer cache A and there (in A instance) resolved the query?. If so, then I think my solution would be configure my protocol in order to transfer quickly the amount of data.

I have a non technical question but I will appreciate very much your advice. Six days ago, I received a mail from Oracle. As I could see, there is a two days seminar about advance performance tuning for 9.2. I am a dba junior, last year I did a four month master in Oracle 9i administration. My problem is that I don´t know if this course is very advanced to me. It treats about index performance,myths about indexes and all this subject matter but I don´t know if it is very soon or very advanced to me. I have been reading your books( now I am re-reading Oracle Expert Architecture) , this very useful forum, articles by M. Rittman and Jonathan Lewis for more than one year but I always have questions and doubts. Oracle training manager has adviced to me that this course is very complex. Tom, please, what would you advice to me?

Thank you Tom, again.



Tom Kyte

Followup  

February 20, 2006 - 8:09 am UTC

It could be that B will be sent to A, it could be that A will send to B little queries of the form "select * from b where y = :bind_variable" as well.

As always "it depends"



Sorry - I don't know what the course you are referring to entails. I cannot comment on whether it would be appropriate for you or not.

Database Link

February 28, 2006 - 12:52 am UTC

Reviewer: Debasish Ghosh from India

I have local database and remote database both are on 10g.

In local database there is two schema with same table. And remote database has also same table (connected via intranet).

I am using oracle 10g developer suit for frontend designing.
My logic is

In local database there is two schema
Local Remote
Schema – A Schema-C
Schema – B

When I insert data into to table abc on local schema A at the same time the same data will be saved on to remote database through database link. If database link not found then the same data will be saved on the second schema on local database. When the connection established then the data transfer from the second schema to remote database.

Here my question is how can I know (remote connection is not found) then the data go to second schema on local database if found then data go to remote database.

I could not trap the when the connection is not established on developer 10g suit.

Thanks for advance



Tom Kyte

Followup  

February 28, 2006 - 7:17 am UTC

why? this is an utterly bad idea. I cannot imagine this in real life. What are you doing?

What action should have take

March 01, 2006 - 12:35 am UTC

Reviewer: D.Ghosh from India

what is other way to save data local & into server at a tile. if link is fail then what action should have taken.

Tom Kyte

Followup  

March 01, 2006 - 8:13 am UTC

"& into server at a tile"?

Insert data locala as well as remote server

March 09, 2006 - 3:37 am UTC

Reviewer: Debasish Ghosh from Calcutta, India

what is other way to save data local & into server at a tmle. if link is fail then what action should have taken.

DG


How to save data into to remote table

March 09, 2006 - 3:41 am UTC

Reviewer: D.Ghosh from India

what is other way to save data local & into server at a time. if link is fail then data should not store into a remote database, after establish the link how I could update remote table with the new row which was not saved due to link failure, but the data has saved in local database.



Getting Error ORA-12154: TNS:could not resolve service name

March 15, 2006 - 7:21 am UTC

Reviewer: Vijay from India

Hi Tom,

I tried to create a database link as follows,

TNSNAMES Entry:

DRP =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = <COMPUTER NAME>)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = DRP.DRP)
)
)

The syntax I have used to create the database link,

create database link DRP
connect to <USER>
identified by <PASSWORD>
using 'DRP'

everything seems to be ok. But still getting the above error. Can you please help me?

Regards,
Vijay

Tom Kyte

Followup  

March 15, 2006 - 5:04 pm UTC

that drp = entry is in the tnsnames.ora file on the SERVER correct, your local copy on your pc is meaningless for a db link.

Using current session on dblink

April 04, 2006 - 8:18 pm UTC

Reviewer: Jairo Ojeda from Costa Rica

I have users that executes my procedures and perform transactions on tables directly through a db link and the audit trail and other logs get the user of the db link (generic user) but I need to get the real database user that perform the transaction not the db link user, where my database is the remote one access by the db link.
To get it, I set a test case where NEMESYS is the remote database,

On remote database: --my database
CREATE USER TEST1 IDENTIFIED BY TEST1 DEFAULT TABLESPACE USERS TEMPORARY TABLESPACE TEMPORAL;
GRANT CREATE SESSION TO TEST1;
CREATE USER SCHEMA2 IDENTIFIED BY SCHEMA2 DEFAULT TABLESPACE USERS TEMPORARY TABLESPACE TEMPORAL;
GRANT CREATE SESSION TO SCHEMA2;
GRANT CREATE PROCEDURE TO SCHEMA2;
ALTER USER SCHEMA2 QUOTA UNLIMITED ON USERS;
create or replace package schema2.pkg_test
as
function pf_plus(pa int, pb int) return int;
end pkg_test;
/
create or replace package body schema2.pkg_test
as
function pf_plus(pa int, pb int) return int
is
li_return int;
begin
li_return := pa + pb;
return li_return;
end pf_plus;
end pkg_test;
/
grant execute on schema2.pkg_test to test1;

On local database:
CREATE USER TEST1 IDENTIFIED BY TEST1 DEFAULT TABLESPACE USERS TEMPORARY TABLESPACE TEMPORAL;
GRANT CREATE SESSION TO TEST1;
CREATE USER SCHEMA1 IDENTIFIED BY SCHEMA1 DEFAULT TABLESPACE USERS TEMPORARY TABLESPACE TEMPORAL;
GRANT CREATE SESSION TO SCHEMA1;
GRANT CREATE PROCEDURE TO SCHEMA1;
ALTER USER SCHEMA1 QUOTA UNLIMITED ON USERS;
CREATE PUBLIC DATABASE LINK DBL_REMOTE USING 'NEMESYS';
create or replace package schema1.pkg_local
as
procedure pp_plus(pa int, pb int);
end pkg_local;
/
create or replace package body schema1.pkg_local
as
procedure pp_plus(pa int, pb int)
is
li_result int;
begin
li_result := schema2.pkg_test.pf_plus@dbl_remote(pa, pb);
dbms_output.put_line('El resultado es: '||li_resultado);
end pp_plus;
end pkg_local;
/

ORA-04052: error occurred when looking up remote object SCHEMA1.SCHEMA2@DBL_REMOTA
ORA-00604: error occurred at recursive SQL level 1
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from DBL_REMOTE

I need to get the database user account of the end user when the end user connects to my database through a db link and the procedure (on my database) that this end user called is called from a procedure on their local database.

Tom Kyte

Followup  

April 05, 2006 - 5:35 pm UTC

does that user exist on the remote database - it would appear not.

You can use dbms_session@remote to set the client id to any string you like on the remote site and that string will be placed into the audit trail as well.

but basically, unless the invoking site tells the remote site "I am so and so" the remote site doesn't "know"

ORA-00904: invalid identifier

April 05, 2006 - 1:52 pm UTC

Reviewer: Kamala iruku from MD

i have select statement which gives some rows with
database link
SELECT a.invoice_id,vendor_id,invoice_payment_id,payment_num,
period_name,amount,bank_account_num,bank_num,discount_taken,Accounting_date,NULL,
a.org_id
FROM
ap_invoice_payments_all@apps_link a, ap_invoices_all@apps_link b
WHERE
a.invoice_id = b.invoice_id
and a.org_id = 62
AND a.last_update_date LIKE SYSDATE - 1;
But, when I put this select statement in the cursor, I am
getting the error
SQL> show errors
Errors for PACKAGE PKG_CELLPOINT_FACT_STAGE:

LINE/COL ERROR
-------- -----------------------------------------------------------------
11/1     PL/SQL: SQL Statement ignored
19/5     PL/SQL: ORA-00904: "A"."LAST_UPDATE_DATE": invalid identifier.

This package is compiled on 8i on windows 2000. I installed
10g Rel 2 on Solaris x86_64.I did the export on 8i and
imported on 10g Rel 2. Import went through without any
problems. The above package got errors. 

Tom Kyte

Followup  

April 06, 2006 - 9:19 am UTC

"a.last_update_date like sysdate-1" - how scary is that! yow, what are you trying to do there???


Not sure why you are getting the error, but thank goodness you are - that needs to be FIXED.

I'm pretty sure you meant to code:

where a.last_update_date >= trunc(sysdate-1)
and a.last_update_date < trunc(sysdate)

(eg: all records from yesterday). Using like - ouch. Implicit conversion of last_update_date to a string. same with sysdate-1. Using the nls_date_format that just happens to be in place!!! ouch.

If the error persists after that change (likely it will) please utilize support to see if there is a known issue with the really really old 8i software.

ORA-00904: invalid identifier

April 05, 2006 - 1:52 pm UTC

Reviewer: Kamala iruku from MD

i have select statement which gives some rows with
database link
SELECT a.invoice_id,vendor_id,invoice_payment_id,payment_num,
period_name,amount,bank_account_num,bank_num,discount_taken,Accounting_date,NULL,
a.org_id
FROM
ap_invoice_payments_all@apps_link a, ap_invoices_all@apps_link b
WHERE
a.invoice_id = b.invoice_id
and a.org_id = 62
AND a.last_update_date LIKE SYSDATE - 1;
But, when I put this select statement in the cursor, I am
getting the error
SQL> show errors
Errors for PACKAGE PKG_CELLPOINT_FACT_STAGE:

LINE/COL ERROR
-------- -----------------------------------------------------------------
11/1     PL/SQL: SQL Statement ignored
19/5     PL/SQL: ORA-00904: "A"."LAST_UPDATE_DATE": invalid identifier.

This package is compiled on 8i on windows 2000. I installed
10g Rel 2 on Solaris x86_64.I did the export on 8i and
imported on 10g Rel 2. Import went through without any
problems. The above package got errors. 

Using current session on dblink

April 06, 2006 - 3:16 pm UTC

Reviewer: Jairo Ojeda from Costa Rica

Thanks for the dbms_session@remote references.

Following the test case,
I created the schema1 user on the remote database, granted the execute on schema2.pkg_test and then schema1.pkg_local on the local database compiled.
The test case works fine and I can get the end user on the remote database.

1. I set the SQLPLUS_PRODUCT_PROFILE to disabled "DECLARE" and "BEGIN" command with SQL*Plus, but If they accesses through dblink, How can I disabled "DECLARE" and "BEGIN" command. --I know that there are other tools to limit but I want to know I can do that to a user that accesses trough a dblink.
2. Can you tell me if I can set something for the schema1 at the remote database to do not permit execute the any package granted --schema2.pkg_test

It is because I need to grant the execute on remote database to let package compiled on the local database, but the only user that can execute my package is the end user not the schema1 user, this user only need the execute privilege to compile their code.

Tom Kyte

Followup  

April 08, 2006 - 8:24 am UTC

1) but - you are NOT accessing the remote database via sqlplus, you are accessing the remote database via a database link!!!!

that product user profile stuff only limits sqlplus and in my opinion should just be ignored these days. The only thing it does is provide a FALSE SENSE OF SECURITY. In the olden golden days - before there was a ton of ad-hoc tools to connect to the database, it *might* have worked. Today in 2006, rather futile to use it.


2) eh?

How to use /*+ driving_site */ if using synonyms to hide dblinks.

April 07, 2006 - 2:58 pm UTC

Reviewer: Rob from Pittsburgh, PA

Tom:

I am using synonyms to refer to my remote tables like this:
CREATE SYNONYM ATTRIBUTE
FOR ATTRIBUTE@dblink;
rather than referencing dblinks in the sql.
I would like to use the driving_site hint since most of the data resides in the remote db. The hint seems to be ignored if you don't have a table@dblink in the FROM clause of the sql stmt. Any tricks to work around this?



Tom Kyte

Followup  

April 08, 2006 - 9:36 am UTC

are you sure about that?

ops$tkyte@ORA10GR2> @test
ops$tkyte@ORA10GR2> /*
ops$tkyte@ORA10GR2>
ops$tkyte@ORA10GR2> drop table t1;
ops$tkyte@ORA10GR2> drop table t2;
ops$tkyte@ORA10GR2>
ops$tkyte@ORA10GR2> create table t1 as select * from all_objects;
ops$tkyte@ORA10GR2> alter table t1 add constraint t1_pk primary key(object_id);
ops$tkyte@ORA10GR2> exec dbms_stats.gather_table_stats(user,'T1');
ops$tkyte@ORA10GR2>
ops$tkyte@ORA10GR2> create table t2 as select * from all_users;
ops$tkyte@ORA10GR2> alter table t2 add constriant t2_pk primary key(username);
ops$tkyte@ORA10GR2> exec dbms_stats.gather_table_stats(user,'T2');
ops$tkyte@ORA10GR2>
ops$tkyte@ORA10GR2> create or replace synonym t2_remote for t2@ora10gr2@loopback;
ops$tkyte@ORA10GR2> */
ops$tkyte@ORA10GR2>
ops$tkyte@ORA10GR2> set linesize 1000
ops$tkyte@ORA10GR2> set autotrace traceonly explain
ops$tkyte@ORA10GR2> select * from t1, t2_remote where t1.owner = t2_remote.username;

Execution Plan
----------------------------------------------------------
Plan hash value: 2842506388

-------------------------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     | Inst   |IN-OUT|
-------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      | 50059 |  5426K|   231   (5)| 00:00:02 |        |      |
|*  1 |  HASH JOIN         |      | 50059 |  5426K|   231   (5)| 00:00:02 |        |      |
|   2 |   REMOTE           | T2   |    34 |   612 |     3   (0)| 00:00:01 | ORA10~ | R->S |
|   3 |   TABLE ACCESS FULL| T1   | 50059 |  4546K|   226   (4)| 00:00:02 |        |      |
-------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("T1"."OWNER"="T2_REMOTE"."USERNAME")

Remote SQL Information (identified by operation id):
----------------------------------------------------

   2 - SELECT "USERNAME","USER_ID","CREATED" FROM "T2" "T2_REMOTE" (accessing
       'ORA10GR2.REGRESS.RDBMS.DEV.US.ORACLE.COM@LOOPBACK' )


ops$tkyte@ORA10GR2> select /*+ driving_site( t2_remote ) */ * from t1, t2_remote where t1.owner = t2_remote.username;

Execution Plan
----------------------------------------------------------
Plan hash value: 861941715

-----------------------------------------------------------------------------------------------
| Id  | Operation              | Name | Rows  | Bytes | Cost (%CPU)| Time     | Inst   |IN-OUT|
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT REMOTE|      | 50059 |  5426K|   231   (5)| 00:00:02 |        |      |
|*  1 |  HASH JOIN             |      | 50059 |  5426K|   231   (5)| 00:00:02 |        |      |
|   2 |   TABLE ACCESS FULL    | T2   |    34 |   612 |     3   (0)| 00:00:01 | ORA10~ |      |
|   3 |   REMOTE               | T1   | 50059 |  4546K|   226   (4)| 00:00:02 |      ! | R->S |
-----------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - access("A2"."OWNER"="A1"."USERNAME")

Remote SQL Information (identified by operation id):
----------------------------------------------------

   3 - SELECT "OWNER","OBJECT_NAME","SUBOBJECT_NAME","OBJECT_ID","DATA_OBJECT_ID","OBJE
       CT_TYPE","CREATED","LAST_DDL_TIME","TIMESTAMP","STATUS","TEMPORARY","GENERATED","SECOND
       ARY" FROM "T1" "A2" (accessing '!' )


Note
-----
   - fully remote statement

ops$tkyte@ORA10GR2> set autotrace off
ops$tkyte@ORA10GR2>
 

Update on ORA-00904: invalid identifier April 05, 2006

April 11, 2006 - 9:30 am UTC

Reviewer: Kamala iruku from MD

I referred the above case to  the oracle support. They
found out that it seems to be bug in 10g Rel 2. Here is
the  test case we did it.The following procedure created
successfully.

create or replace procedure a is
v_date date;
CURSOR CUR_AP IS
SELECT select sysdate from dual@apps_link;
begin
open cur_ap;
fetch cur_ap into
v_date;
close cur_ap;
end;

Procedure created.

But, when I tried to create procedure

1 create or replace procedure a is
2 v_invoice NUMBER(15);
3 CURSOR CUR_AP IS
4 SELECT invoice_id from ap_invoices_all@apps_link;
5 begin
6 open cur_ap;
7 fetch cur_ap into
8 v_invoice;
9 close cur_ap;
10* end;
SQL> /

Warning: Procedure created with compilation errors.

SQL> show errors
Errors for PROCEDURE A:

LINE/COL ERROR
-------- --------------------------------------------------------
4/2 PL/SQL: SQL Statement ignored
4/9 PL/SQL: ORA-00904: "INVOICE_ID": invalid identifier

Oracle support answer for this!!!

This is a new bug still in description phase as development has yet to reproduce even though the support engineer was able to reproduce with the customer'
s testcase. Although the bug is not yet public since it hasn't been accepted by development as a bug,As it appears the workaround is acceptable for you at least for now.


PROBLEM:
--------
App which worked in 8i and 9i (9.2) is failing in 10.2.0.2.
In short, the problem is that an update using a synonym for a remote table 
(dblink) fails with ORA-904.
.
The long version is that their PLSQL app appears to be making updates when it 
is not because of this ORA-904 condition.
The testcase provided below demonstrates all of this.
.
.
DIAGNOSTIC ANALYSIS:
--------------------
Ran the testcase against 10.2.0.2 databases and saw the same behavior.
Also ran the testcase against 9.2.0.6.0 databases and the problem did not 
occur (did not test this against 10.2.0.1).
.
Also noted that by referencing schema.table@dblink, instead of synonym, the problem does not occur.
WORKAROUND:
-----------
Call schema.table@dblink instead of synonym. This is unacceptable as it 
requires a code change for their application.



 

DB Link Names

April 17, 2006 - 3:59 am UTC

Reviewer: Kiran Kumar from India

Tom,

Is there any specific naming conevtion has to be followed while creating DB links, I saw some of the topics in this site on Global Name convention, do we have to create DB link with the same name as Global Name ? please explain me this topin in detail.


Thanks and Regards
Kiran

Tom Kyte

Followup  

April 17, 2006 - 8:04 am UTC

have you checked out the documentation first? We explain things in detail in there. It is a convention - if you have global names set to true (good idea), then the dblink name must incorporate the remote databases global name - so as to avoid confusion and have unique names for all distributed databases.

Bidirectional dblinks not recommended?

April 20, 2006 - 10:23 pm UTC

Reviewer: Shawn Kim from Korea

Hi Tom,

I have 2 databases (A and B) and 2 WAS per each(WAS_A and WAS B).
Database A has a table A_TBL and database B has the similar table B_TBL
totally same columns but simialr table name and totally different data.

I'like to create 2 dblinks, one from A to B and the other one from B to A.

I expect that any WAS of two can generate same ouput by queries as follows..

WAS_A with database A
====================
select * from A_TBL where ...
union all
select * from B_TBL@B where ...

WAS_B with database B
====================
select * from A_TBL@A where ...
union all
select * from B_TBL where ...

But I hear that bidirectionl dblinks are strongly not recommended from DBA.
Is that true? if so why?



A lot of thanks

Shawn Kim


Tom Kyte

Followup  

April 21, 2006 - 7:26 am UTC

"WAS"?


as the DBA why - these are not "bi-directional dblinks", this is

a) database A needs to query B, therefore A must have a dblink to B
b) database B needs to query A, threefore B must have a dblink to A

sounds like "fullfillment of requirements" to me.

fullfillment of requirements

April 21, 2006 - 10:22 am UTC

Reviewer: Shawn Kim from Korea

Thanks a lot,Tom.

Sorry for my poor English;;

In Korea, "WAS" is a usual abbreviation of Web Application Server such as WebLogic..(perhaps that makes sense only in Korea..)

bi-directional is another poor English just to say a) and b).

I understand that you say there is no problem for dbliks like that.right? I will ask the dba why the hell he does not recommend again tomorrow.

Thanks..



Tom Kyte

Followup  

April 21, 2006 - 3:28 pm UTC

That is the problem with abbrevations - which as I get older, I am swearing off of (without first defining them on the same page)...


That is the way database links are designed to work, yes.

Up to Date Data

April 24, 2006 - 4:46 am UTC

Reviewer: Nikhilesh from INDIA

Dear Tom,
We got a mail from our DBA for following problem and he is seeking for solution.Could you please comment on this.

Background :


A) AT&T has a BO reporting tool which extracts reports from CSG database
B) To avoid performance penalty, they backup the data from production server and restore it on a report server daily at night. This makes the reporting server information 1 day old, as they do this activity once a day.

C) Now they want the information to be more up-to-date, as much as possible.

The primary database is of approximately 28GB size. There is one more database separately created for Reporting purposes.


Problems :

The datatypes used in this application are BLOBs and CLOBs in majority. We have explored following options :
1) Materialized view or snapshots result in an error saying CLOBs and/or BLOBs are not supported over the db-link

2) While investigating Logical Standby option, we came across few columns (around 44) which were appearing as not supported. All these columns belong to the tables which are must for the reporting purposes.

3) Replication is not supported with BLOBs and CLOBs.



Tom Kyte

Followup  

April 24, 2006 - 5:45 am UTC

1) that is not correct, blobs and clobs are supported
2) but you don't tell me what they are!
3) false



But actually, I don't see why you wouldn't use a single database. Hypothetical performance issues aside.

Tuning distributed query

April 24, 2006 - 11:49 am UTC

Reviewer: A reader

Hi, Tom,

I have a question about tuning distributed query.
I have a distributed query that starts from a front end database, say FE, and spread work to various back end databases on other servers, say BE1, BE2, etc.
I created database links from FE to BE1, BE2, etc and named as BE1, BE2, etc.
Each BE database has the same schema structure, just having different data. Don't ask me why not use partitioned table on a single schema, it's not my decision. What's done is done.
So we have a view on FE database as a union all of all corresponding tables on BE databases.

Create view V1
as
select * from t1@BE1
union all
select * from t1@BE2
union all
select * from t1@BE3
...

My distributed query is third party tool generated, quite complicated, but will boil down to something as simple as this:
select * from v1 where c1 in ('somevalue', 'somevalue2')

I want the CBO to rewrite the query *consistently* as
select * from t1@BE1 where c1 in ('somevalue', 'somevalue2')
union all
select * from t1@BE2 where c1 in ('somevalue', 'somevalue2')
union all
select * from t1@BE3 where c1 in ('somevalue', 'somevalue2')
...
This way, the predicate is consistently passed onto BE databases to spread out CPU and IO.
It also means I don't want Oracle to pull all data in t1 from various BE databases into FE memory and ran filter there. Moreover, I would like to be able to achieve pushing group by into BE machines, if that's possible.
Materialized view is not an option for me.
Is there a way to do just that?

Thanks,


Insert and driving_site

May 26, 2006 - 7:56 am UTC

Reviewer: Andrey V. from Russia

Is the remote view the only way to join tables on remote site in case of insert?

It requires create view and create database ling privilege on remote site, and what if I'm not able to create objects or links there? I'm suffering from such problem too - remote table is about 200Mb and local is very small = to join this tables in insert .. select .. statement Oracle always use full remote table download to local site(regardless to driving_site hint)

Thank you...

Tom Kyte

Followup  

May 26, 2006 - 8:58 am UTC

it does not require create database link privilege - you already HAVE the dblink.

create view is pretty much mandatory if you want to use dblinks in my opinion.


or how about a global temporary table on the remote site.

Dblink Session

May 27, 2006 - 9:35 am UTC

Reviewer: reader from india

Hi,

I want to identify the remote connections which are being
made using db_links.


Thanks,



Not sure

May 29, 2006 - 4:09 am UTC

Reviewer: Andrey V.

Sorry Tom, I'm not sure that I understood it well. Why I don't need "create db link" privilege? Do I have to create view on local site? It doesn't work because when I use insert it makes no difference. And on remote site, I have no database link(it's not defined in remote server dictionary).
This is common situation I think when people create database link to schema that has only create synonym privilege and some select privileges to certain tables. Objects on remote database are owned by another user. So "create global temporary table" is not possible and "create view" as well.
Do you think it would be the best approach in this case to pass local tables to remote site as a list of values?



Tom Kyte

Followup  

May 29, 2006 - 7:44 am UTC

You don't need create database link (some else creates that, you wouldn't be creating it on the fly or on a recurring basis, no need for YOU to have it)

Also, in most cases you would not need a dblink at all - you just need create view.

across network,

June 06, 2006 - 5:47 pm UTC

Reviewer: A reader

I have two questions.

1. If we are doing INSERT..SELECT while SELECT is performing select using a DB LINK, is there a way to find out how much data is coming through the network in a particular duration (say in one minute).

2. Is there a way to know when was the last commit/rollback happened on a particular table?

Resolution of pseudo columns in a query to Remote database

June 20, 2006 - 4:00 pm UTC

Reviewer: Baiju from India

Hi Tom,

What will be the output of

select sysdate from sys.dual@remote_db

consider the database pointed by remote_db is running on a different timezone. :) :)

Thanks,

Baiju



Tom Kyte

Followup  

June 21, 2006 - 9:48 am UTC

sysdate comes from the local database.

If you want sysdate to be remote, you can create a view on the remote site and query that.

SYSDATE from Database Link

June 29, 2006 - 5:23 pm UTC

Reviewer: Tim from PA, USA

Thanks for the info on using a view for getting the server time from across a link.

Before we saw this - we had tried using a function and it didn't work - returned the local time. I was wondering if you knew why? I would have thought that the function would have acted in a similar manner as the view - at least in this respect - ie, return the remote server time.

CREATE OR REPLACE FUNCTION remote_sysdate
return date
is
begin
return sysdate;
end;
/

We put the above function on both sides of the link and then execute:

select
(select to_char(remote_sysdate,'dd-MON-yyyy hh24:mi:ss') from dual) time_local,
(select to_char(remote_sysdate,'dd-MON-yyyy hh24:mi:ss') from dual@Remote_DBLink) time_remote,
((select remote_sysdate from dual) - (select remote_sysdate from dual@Remote_DBLink)) days_diff
from dual;

The time returned was clearly the local time. (Using a view as you suggested returned the time difference between the two systems with no problems.)

Thoughts?

Thanks.

Tom Kyte

Followup  

June 29, 2006 - 6:50 pm UTC

where does the function "remote_sysdate" reside?

SYSDATE from Database Link

June 30, 2006 - 11:00 am UTC

Reviewer: Tim from PA, USA

We created the function on both sides. The one server is 8.1.7 and the other is 9.2.0.4. As I mentioned - that view you suggested - works great. I was just confused as to why the same concept using a function did not work.

Tom Kyte

Followup  

June 30, 2006 - 12:46 pm UTC

I don't see you calling the remote function though?


select
(select to_char(remote_sysdate,'dd-MON-yyyy hh24:mi:ss') from dual)
time_local,

that was the local function 'remote-sysdate' against the local dual table..

(select to_char(remote_sysdate,'dd-MON-yyyy hh24:mi:ss') from
dual@Remote_DBLink) time_remote,

that ran a remote query against dual, got a row back and then invoked the local function remote_sysdate

((select remote_sysdate from dual) - (select remote_sysdate from
dual@Remote_DBLink)) days_diff
from dual;

that just combined the two from above - but BOTH are the local function


just like "select sysdate from dual@dblink" runs the "local sysdate" function, select remote_sysdate from dual@dblink - runs the local remote_sysdate function.


You would just

exec :x := remote_sysdate@dblink;


run the REMOTE function.

SYSDATE from Database Link

June 30, 2006 - 12:55 pm UTC

Reviewer: Tim from PA, USA

Thanks. I pretty much feel like an idiot now...
:)
Although in my defense - two other people also looked at this - and we all missed it. I guess sometimes you see what you want to see.
Again - thanks.

Views across database links

July 11, 2006 - 7:08 pm UTC

Reviewer: Tim from PA, USA

Another followup on the database link if you don't mind.

Further up on this page you have suggested that it is your preference to use views to encapsulate table via link reference (if I have read correctly).

I would like to be able to do this.

We have two database instances both on Oracle 9.2.0.4. Using your suggestion, I would like the view to be stored once in a single schema and allow several user accounts to access the view (which Oracle then goes across the link to get the data).

However, I am having a problem in getting this to work. The SQL used to create the links and user/schema accounts is shown followed by a cut-n-paste from SQLPlus.
Could you please explain why I am getting the ORA-00942 / ORA-00942 error?
Thanks.

Create public database link QFN8DEV2
using 'QFN8DEV2';

Create public database link QFN8TST
using 'QFN8TST';

sc_schema and sc_user created in both local and remote database instances.


CREATE USER SC_SCHEMA
IDENTIFIED BY VALUES SQUIRREL42
DEFAULT TABLESPACE mytablespace
TEMPORARY TABLESPACE DBTEMP
ACCOUNT UNLOCK;
GRANT CREATE VIEW TO SC_SCHEMA;
GRANT CREATE TABLE TO SC_SCHEMA;
GRANT CREATE SESSION TO SC_SCHEMA;
GRANT CREATE SYNONYM TO SC_SCHEMA;
GRANT CREATE TRIGGER TO SC_SCHEMA;
GRANT CREATE SEQUENCE TO SC_SCHEMA;
GRANT CREATE PROCEDURE TO SC_SCHEMA;
ALTER USER SC_SCHEMA QUOTA UNLIMITED ON mytablespace;

CREATE USER SC_USER
IDENTIFIED BY VALUES MOUSE24
DEFAULT TABLESPACE mytablespace
TEMPORARY TABLESPACE DBTEMP
ACCOUNT UNLOCK;
GRANT CREATE SESSION TO SC_USER;




sc_schema@QFN8DEV2>
sc_schema@QFN8DEV2> @connect sc_schema@qfn8tst
Enter password: ********
Connected.
sc_schema@QFN8TST> create table t_foo4
2 as select * from all_objects
3 where rownum < 100;

Table created.

sc_schema@QFN8TST> grant select on t_foo4 to sc_user;

Grant succeeded.

sc_schema@QFN8TST> @connect sc_schema@qfn8dev2
Enter password: ********
Connected.
sc_schema@QFN8DEV2> create view v_foo4
2 as select * from t_foo4@qfn8tst;

View created.

sc_schema@QFN8DEV2> select count(*)
2 from v_foo4;

COUNT(*)
----------
99

1 row selected.

sc_schema@QFN8DEV2> grant select on v_foo4 to sc_user;

Grant succeeded.

sc_schema@QFN8DEV2> @connect sc_user@qfn8dev2;
Enter password: ********
Connected.
sc_user@QFN8DEV2> select count(*)
2 from sc_schema.t_foo4@qfn8tst;

COUNT(*)
----------
99

1 row selected.

sc_user@QFN8DEV2> select count(*)
2 from sc_schema.v_foo4;
from sc_schema.v_foo4
*
ERROR at line 2:
ORA-00942: table or view does not exist
ORA-00942: preceding line from QFN8TST


sc_user@QFN8DEV2>


Tom Kyte

Followup  

July 12, 2006 - 3:31 pm UTC

add the schema name to the view - not just t_foo4, sc_schema.t_foo4.

Views across database links

July 12, 2006 - 5:03 pm UTC

Reviewer: Tim from PA, USA

Excellent !!!
Thanks - this will work very nicely for us. I don't understand why the schema name is necessary in the view definition - but I am willing to roll with it. I appreciate your time on this.
:)

Tom Kyte

Followup  

July 12, 2006 - 5:48 pm UTC

a view is stored sql...

you are using "current user dblinks"

depending on WHO is logged in, that is WHO gets logged into the remote site. That is the "current schema" over there.

select on user.table to diffuser on remote db

July 24, 2006 - 12:18 pm UTC

Reviewer: jas

I want to grant select on user.table to diffuser on remote db.

how can I give that.
I dont want to grant it to public

Tom Kyte

Followup  

July 24, 2006 - 2:49 pm UTC

just grant it? not sure what you mean.....

just grant select on the table to the user(s) you want to have select on it.

it doesn't works

July 24, 2006 - 3:48 pm UTC

Reviewer: A reader

error is no user or role present

Tom Kyte

Followup  

July 24, 2006 - 4:19 pm UTC

umm, context?

no idea what you mean. lay it all out. be specific, be precise. pretend you are trying to explain your problem to your mom (whose theoretically doesn't work in technology)

oracle report

July 25, 2006 - 10:54 am UTC

Reviewer: Alex smith

Hi tom,
I'm getting very strange problem. Actually i'm running my oracle report (10g) using application server, report server. The report is originated from Jave script screens but instead of printing '£' symbol it prints '$' sign. To get this sign I'm using following select stmt.

select to_char(1234,'L99,99') from dual;

could you please advise me what is going wrong?

Thank,
Alex Smith


Tom Kyte

Followup  

July 25, 2006 - 11:58 am UTC

nls settings, specifically - nls_currency.

it is set to $ apparently

ora-2054,ora-2068,ora-12571

August 07, 2006 - 9:10 pm UTC

Reviewer: A reader

I don't know this is right place for my question!But I hope tom or someone help me to resolve it.

My question:

ServerA: table_name A
ServerB: table_name B
Database link ServerA to ServerB : a_b_link

Now I have a trigger.When I insert a row into A on ServerA,it automate insert it into B on ServerB.But when ServerA to ServerB's network disconnect,it raise error ora-2054,ora-2068,ora-12571,I want catch these error and handle it,but I don't kow hot to do it.

create or replace trigger a_ait
after insert on a
for each row
begin
insert into a@orcl_link values (:new.x,:new.y);
/*
How do I catch these exception because network disconnect here????

when ... then
insert into a_bak values (:new.x,:new.y);

*/
end;

Thanks in advance!!!!!
regard Tom-kyte.

Tom Kyte

Followup  

August 08, 2006 - 7:34 am UTC

not all exceptions are catchable.

if you use pragam exception_init and map those error codes, can you catch them?

nmgzw

August 10, 2006 - 4:08 am UTC

Reviewer: nmgzw

thanks very much for your regard response!!!

I have try it.But it can't catch these error!
If I don't other method to catch it??

thanks!!!

Tom Kyte

Followup  

August 10, 2006 - 9:14 am UTC

not all are catchable.

the client will get this one.

August 10, 2006 - 8:51 pm UTC

Reviewer: nmgzw

I understand your valuable answer.
thanks very much!!

tnsnames.ora

August 11, 2006 - 11:41 am UTC

Reviewer: sam

Tom:

Is the file tnsnames.ora created per machine or database installed on machine?

I have one unix server that will have 3 instances/databases (A,B,X) on it. Can I have one link "my_link" in database A pointing to a database "X" on same machine while the same link name "my_link" ceated in Database B pointing to a database "X" on different machine on network ?

Thank you,

Tom Kyte

Followup  

August 11, 2006 - 12:19 pm UTC

it is a client thing, it most often is on a machine WITHOUT a database.

You can have one
You can have dozens
You can have zero

what would you like?


(ps: one unix server should have AT MOST one instance on it).

db links

August 11, 2006 - 3:35 pm UTC

Reviewer: sam

Tom:

I am confused.

1. I thought everytime you install oracle server you will have one tnsnames.ora on the server itself? Correct. I think when you have a plsql program that has a statement like;

select * from table@my_link;

then it looks in the tnsnames,ora to find out the server/database where that table is.

2. When you have a machine that wants to connect to the database, you install oracle client on that machine and create also another tnsnames.ora file on the client. When the client like SQL*plus or SQL*navigator tries to connect it also looks at the "service name" on the server (tnsnames.ora) before it allows you in?Correct

3. I think you can have same link name in two databases that are pointing to different service name with each pointing to different machine?Correct.

Tom Kyte

Followup  

August 11, 2006 - 3:41 pm UTC

1) you don't have to

the tnsnames.ora can be located centrally and discovered via the TNS_ADMIN environment variable (I have installs of oracle from 7.3 on up on a single test machine - one tnsnames.ora in /var/opt/oracle)

2) you don't have to (have a tnsnames). You could use the connect string directly, you can use a directory service, you can use a network share for a single tnsnames.ora.

3) sure.

how can i posting question in AskTom.Com

August 15, 2006 - 10:59 pm UTC

Reviewer: maxzsim from SINGAPORE

Hi ,

i want to post questions here but how can i do that ?

pls advise
tks & rdgs

Tom Kyte

Followup  

August 16, 2006 - 8:22 am UTC

wait until I'm taking them - see home page, it says when I'm not taking them (and why) and when I am

Tom is the greatest!

August 17, 2006 - 10:02 am UTC

Reviewer: Ben Buckley from Fort Worth, TX

Tom,
Your answers are complete, straightforward and accurate. You are the GREATEST!!!

Atypical problem

August 20, 2006 - 6:33 am UTC

Reviewer: Arindam Mukherjee from Kolkata, India

Respected Mr. Tom,

Just now, I have got one problem of calling one function through Database link. SOMETIMES it takes too LONG and sometimes it gives result too fast. Is it possible programmatically to wait for a specific time frame say 20 seconds and after that if the result does not reach us, we cancel that call of that function and the program goes along another route. Well, since my English is not smart enough, I would like to portray it through pseudo code as follows.

Time t : = 0;
Number a := 0; /* Initialization*/

UNTIL t <= 20 sec.
{
Number a: = calling remote function through dblink.
}

If a != 0 then /* Remote Function call successful */

End if;

If a = 0 then /* 20 sec over but function calling is not successful */

End if;

Please help me. I am really in dire need of this solution. Kindly give me full executable code, not psuedo code like me.


Tom Kyte

Followup  

August 20, 2006 - 8:15 am UTC

No there is not.



link

August 22, 2006 - 4:26 pm UTC

Reviewer: sam

Tom:

I am trying to connect from a new 9i instance "ABCP" to an old 8i instance "ABCP".
DBA created this entry in the tnsnames.ora.

OLDABCP.company.com =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOTCOL = TCP)(HOST = www.company.com)(PORT = 1521))
    )
    (CONNECT_DATA = (SID = abcp)(SERVER = DEDICATED))
  )

When I create a db link using that TNS service name, it gets created but when I use it it gives me this error. Do you know what is happening.

  1  create database link test
  2  connect to abcadmin identified by abcadmin
  3* using 'oldabcp'
SQL> /

Database link created.

SQL> select * from dual@test;
select * from dual@test
                   *
ERROR at line 1:
ORA-12538: TNS:no such protocol adapter
 

Tom Kyte

Followup  

August 27, 2006 - 3:11 pm UTC

try this:

using '(description=(address_list=(......';


and tell us if it reproduces, if not - the dba updated the tnsnames.ora file for you.

What about DB_LINKS which are not public?

September 05, 2006 - 2:12 am UTC

Reviewer: A reader

Hi Tom,
I am presently trying to fine tune a package.
As it happens the package has a db_link defined in it which references a remote table.

The structure is as follows:
Normal User:
....
Package and Package Body
Database Link
.....

DBA: My ID

Now as it happens, i wish to see if the database link is active or not. But i do not want to connect as the Normal User and then test the connection. Another way is to create a db_link similar to that one and sfter testing it i can drop that. But that is not the idea. Also assume that i do not know the password of that user.

I have the DBA privileges, in addition to that what other privs do i need.
Please advise,
Oracle Version 9i Release 7
HP-UNIX
Thanks as always


Tom Kyte

Followup  

September 05, 2006 - 4:51 pm UTC

I am not following you here. How would connecting as the "normal user" tell you if the link was "active" - define "active" for me here.

Sorry for the confusion..

September 06, 2006 - 12:22 am UTC

Reviewer: A reader

Hi Tom,
Sorry for the misinformation.
Let me be a bit more precise.

A user, say 'X' has a db_link in its schema called, "remote_db". Please note that this db_link is not public.
Now, my user, which has the DBA privs, wishes to check the db_link is working.
So, my question is how do i check the db_link X.Remote_db.
Please bear in mind the following points:
1. I have no access to the remote db.
2. The Remote_db uses a connect to clause.
3. I do not know the pwd of the user X nor of the user defined in the connect to clause of the db_link.

I tried using current_schema=X but, in vain.
Oracle 9i Rel 7

Please advise.

Tom Kyte

Followup  

September 06, 2006 - 7:49 am UTC

you will have to "become that user".

That is something the DBA can definitely do.

Glad to know that a DBA can...

September 07, 2006 - 1:48 am UTC

Reviewer: A reader

Hi Tom,

I am relieved to know that a DBA can accomplish the same.
But a hint or an example would havein appropriate :)

I scoured thru the docs but could not find anything.

Thanks as always.

Tom Kyte

Followup  

September 07, 2006 - 7:08 am UTC

</code> http://asktom.oracle.com/Misc/su.html <code>

Sorry for the low Stars...

September 07, 2006 - 7:34 am UTC

Reviewer: A reader

Hi Tom,
Couldn't help it.
I know of that approach. But in my prior post i had asked you if you know of any other approach.
As it is production i do not want to change the password and set it back.
Of course exp/imp is another way.
But way too hectic.
Can it be done like select * from <user>.table;
I want a similar approach..
Login as myself and check the db_link thats it.
As far as i know it is not possible. Or is IT?? :)



Tom Kyte

Followup  

September 07, 2006 - 8:19 am UTC

exp/imp isn't "another way"

I'm telling you the way, sorry you don't like it.

Copy data for a few tabes from one DB to the other

September 08, 2006 - 5:07 pm UTC

Reviewer: A reader

Tom,

We are planning on putting a DBLink between 2 Oracle DB's. This DBlink will be used to get customer and vendor data from DB1 to DB2. Triggers on DB1 will be used to copy data from DB1 to DB2 (after update, insert, delete etc.). The number of customers/vendors that get created daily is about 10000. Total no of tables where the triggers may have to be put in is about 10. Both the DBs are in the same physical location.

I would like to know
1) If the DBLink or the trigger is going to put additional load on the source system (DB1) or destination system (DB2). Additional as in slowing down perforamance noticably.
2) What is the best way to copy data in such situations?

Thank you




Tom Kyte

Followup  

September 09, 2006 - 12:07 pm UTC

that would be the wrongest way to do it.


please read about materialized views.

Copy data for a few tabes from one DB to the other

September 10, 2006 - 12:28 am UTC

Reviewer: A reader

Thank you Tom - I will be reading about Materialized views. But the situations where the db links are already present (data coming from db1 to db2 through triggers/dblinks).

1) Will the presence of a dblink impact the source system?
2) Is there a rule of thumb reg. using dblinks and Materialized views?

Thank you Tom for the valuable advice


Tom Kyte

Followup  

September 10, 2006 - 9:27 am UTC

1) only if you do something through the dblink, if you don't use it, it is just metadata and doesn't do a thing

2) ROT is ROT (rule of thumb), meaning no, there are not ROT's that are universally applicable.

another ORA-02019 question

September 19, 2006 - 2:51 pm UTC

Reviewer: Jim from Phila, PA

Hi Tom, I have a slightly different db link problem:

I have a user a who owns 2 db links, db1 and db2 and two views which point to b.t1 and c.t2 These views are used as an access layer to the two tables b.t1 and c.t2 for developers
create view a.v1 as select * from b.t1@db1
create view a.v2 as select * from c.t2@db2

There is a developer, d who has select, insert,update and delete on a.v1. d can do the following:
select * from a.v1
select * from a.v2
insert into a.v1 values (...)

but d gets an ORA-02019 when he tries
insert into a.v1 select * from a.v2 where ....

how is db link db2 being evaluated?



Tom Kyte

Followup  

September 19, 2006 - 3:28 pm UTC

see
</code> http://asktom.oracle.com/pls/asktom/f?p=100:11:::::P11_QUESTION_ID:1281675938015#72180822649625 <code>



the corporate wating line

September 20, 2006 - 2:06 pm UTC

Reviewer: Jim from Phila, PA

I have put in a request to add the tns entries to the two servers in question, I expect that the problem will be gone once that is done.
Missed you at SIG, had a query to tune ( 50 min down to 30 sec, thank you Cary!)
Thanks!

How to find the objects which created by db link?

September 25, 2006 - 5:25 pm UTC

Reviewer: A reader from NY, USA

Tom,
If I created the table via database link as below, how can I know it was using database
link later? *_tables, *_objects has no db link information(only in *_synonyms). Please provide the query or dictionary name.

AUCTIONET@anetdev > select DB_LINK ,host, USERNAME from user_db_links;

DB_LINK
--------------------------------------------------------------------------------
HOST
--------------------------------------------------------------------------------
USERNAME
------------------------------
AUCTIONET_MIRMVU
dev1
MIRMVU

AUCTIONET@anetdev > create table test_link as select * from MVU_EXCHANGE_RATES@AUCTIONET_MIRMVU
2 where 1=2;

Table created.

Thanks very much!


Tom Kyte

Followup  

September 26, 2006 - 2:27 am UTC

you cannot, it is not anything we would "remember".

Simple but firm answer

September 26, 2006 - 10:21 am UTC

Reviewer: Reader from NY,USA

Tom,
Thanks for the response.This is the answer what I want to confirm from you. I could not find any dictionary to get db link information in SUCH case above(if create synonym for remote database object via db link, then we know the db link from *_synonyms). But it is not MY case. I thought maybe there is some dictionary for my case, so I posted the above question. Now I am clear.


Tom Kyte

Followup  

September 26, 2006 - 3:54 pm UTC

well, just to clarify - because you confuse me here - the sql used in the create table as select... is not stored...

however the dblinks and all are

but if you are looking for the original sql used in the create table as select, we don't have that (well, auditing could have captured it, but not by default)

RE: Another ORA-02019 question

September 27, 2006 - 1:09 pm UTC

Reviewer: Jim from Phila, PA

This is a followup on my previous question.
I have verified that the tns entries are on both remote servers. I am still getting the 02019 when I insert into t1@d1 using select t2@d2.
The db link d2 does not exist on the db referenced by db link d1.
My original question still remains, where is db link d2 evaluated?
on the db referenced by db link d1, since that is where the select is done? if so do I have to have db linnk d2 defined there?
it obviously is not done on the db where the insert statement is submitted because I can select from t2@d2 on that database.


Tom Kyte

Followup  

September 27, 2006 - 4:18 pm UTC

the database link is resolved by the dedicated server that is "running" that query.

so the dedicated/shared server and its "environment" will resolve that dblink.

so, if you use a shared server (environment comes from whomever started database)

so, if you use a direct dedicated server (forked from YOUR process, no net)... (environment comes from YOUR environment)

so, if you use a dedicated server from the listener - (environment comes from listener)

and TNS_ADMIN could be different for all three....


you could always use the (description=.....) instead of a tnsname connect string in the create database link to remove any ambiguity.

Resultset via db-link versus DB2

October 05, 2006 - 9:42 am UTC

Reviewer: Franco Perego from Italy

Hi Tom,

the DB2 administrator release a series of stored procedures in the DB2 database to access large volume of data. The result of those procedure is a result set. Is there a way to call those procedures from Oracle (10g2) using a db-link and read the result set?

Thanks in advance,
Franco Perego


Database Link and security

October 25, 2006 - 12:14 pm UTC

Reviewer: MS from USA

Oracle Release 9206
global_names=true

Tom,
We have a development group that does the data updates in production.
My question is regarding methods to grant them this kinda temporary maintenance access on certain production tables:
1. Grant the access through a link (password protected)...and let them do updates from the dev database.
2. Create a maint account in production db..and let them do the maint. there..
3. Tom's way

What woud be your choice and why?

Thanks a bunch..and hope you are having fun at the open world..


Tom Kyte

Followup  

October 25, 2006 - 2:03 pm UTC

3) they develop the processes that are fully tested in development and then these processes are installed and run in production by the appropriate individual - which may well be the DBA (might not be the dba, that is a matter of policy)

I would not be giving access from the dev db to the real production instance.

requirement,

October 26, 2006 - 5:01 pm UTC

Reviewer: A reader

I have a database DBS_DEV. Is there a way to know what all databases have a DB link to DBS_DEV database?

thanks,



Tom Kyte

Followup  

October 27, 2006 - 7:28 am UTC

no, you would have to go to those databases and see if they have any links, there are no cross database dependencies set up.

where it will fetch data

November 01, 2006 - 8:10 am UTC

Reviewer: Parag J Patankar from India

Hi Tom,

Suppose I am 2 databases on two different servers, A and B. From B I have created db link to access database on A.

Now suppose I have written a query on server b to access tables of server a using dblink where my query will get processed ? Where will be db blocks of these two tables will be stored ? On Server A or Server B ? Kindly explain.

thanks & regards
PJP



Tom Kyte

Followup  

November 01, 2006 - 8:51 am UTC

by default, B would parse and optimize this query, generate SQL to send to A to request data, A would process it's bit of sql (caching it's blocks in its buffer cache" and return data to B, B would (if needed) stash that information in your UGA/PGA (private memory) and process it further, ultimately returning the data to you.

Error while accessing tables using DBLINKS

November 02, 2006 - 2:41 am UTC

Reviewer: Gowrish from India

I have 2 Oracle database (10.2.0.1.0) running on two servers
and both have the same username and the passwords are identified externally
ie.,
Create user ops$graphix identified by externally.

 I have created database link to connect to other sever 

Create database link dblink using ‘secondary’;

 When I select say

Select * from dual@secondary; 

It throws the following error

ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from EGSECONDARY

But I am able to connect to the remote by
SQL> /@secondary
 
In init.ora in remote database  I have set the 
remote_os_authent=true
os_authent_prefix=ops$
remote_login_passwordfile=’EXCLUSIVE’ and also tried with = NONE

Please help.
 

Tom Kyte

Followup  

November 02, 2006 - 7:05 am UTC

you do not use OS authentication over the dblink (your oracle backend is not running with your credentials after all)

please get rid of that os_authent - ouch (I think I'll just drop a machine into your network running unix and create an account, yah, that's the ticket).  turn that off NOW.

alter user ops$graphix identified by SOME_PASSWORD;

ops$graphix can still connect / locally
ops$graphix can identify themselves securely over the network (including dblinks)
 

Error while accessing tables using DBLINKS

November 02, 2006 - 7:39 am UTC

Reviewer: Gowrish from India

Thanks a lot Tom for you inputs

long time to connect to the database

November 04, 2006 - 10:39 am UTC

Reviewer: Dawar Naqvi from Los Angeles, CA USA

OS: IBM/AIX 5.2 Unix
DB: 10.2
Client: 10.2
Tools: SQLPLUS, Enterprise Manager Studio

Tom,

It takes long time to connect to the database. (50 sec)
Once its connect to the Database, its work fine.

we tested connection via client using tools such as SQLPLUS & Enterprise manager studio.

We have some other server (same as above) on the network running same DB version are fine.
And takes less time to connect to the database through client.

What should be check from Database site?

Any feed back will be appreciated.

cheers,
Dawar

Tom Kyte

Followup  

November 04, 2006 - 12:31 pm UTC

sounds like DNS problems could be here.

if you replace the hostname in your tns connect string with a static IP address, what then

connection to the DB

November 04, 2006 - 1:02 pm UTC

Reviewer: Dawar Naqvi from Los Angeles, CA USA

Tom,

Here was my tnsnames entry from server.

SID =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST =fully-qualified-name)(PORT = 1521))
(CONNECT_DATA =
(SERVER = DEDICATED)
(SERVICE_NAME = sid)
)
)


Prior to changes, It took 61 sec to get connected.
So I repaced " fully-qualified-name" with IP address.

Then It took 30 sec to connect.

But we have one more server on same location.
sqlplus connection is right away. (normal)
Its using fully qualified name in tnsnames.ora at server site.
But its fine with that.

cheers,
Dawar




Tom Kyte

Followup  

November 04, 2006 - 2:45 pm UTC

might therefore be time to take a look at your network if simply using an IP address cut 50% of the connect time - remove Oracle from the equation for a minute and make sure your networking is networked right.

ORA-03106 Error with DBlinks

January 08, 2007 - 7:56 am UTC

Reviewer: Karthik from Chennai,India

Hi Tom,

I have several procedures which connect to a different database through database link.I imported this dump in a new machine. I'm not able to compile only those procedures which use this dblink. All other procedures are compiling properly.SQL queries which use this DB link also run correctly.

For eg:

select * from emp@production
gives me no errors. When I use this query inside a procedure, this procedure doesnt compile and the error points to the DBlink.I get this error message

ORA-00604: error occurred at recursive SQL level 1
ORA-03106: fatal two-task communication protocol err

What could be the issue?

Thanks in Advance,
Karthik


Tom Kyte

Followup  

January 08, 2007 - 1:05 pm UTC

likely version related - please utilize support.

Comparing Views with Synonyms

January 30, 2007 - 12:22 am UTC

Reviewer: Raj from India

I am currently working on a 8.1.7.4 database which has db links with 7.3.4 database. All the dblinks are running fine.

But the 8.1.7.4 database is now getting upgraded to 9.2.0.8 and so I am planning to use the 8.1.7.4 as the 'middle-man' between 9i and 7 databases.

Now, to fetch the data from 7 database which among synonyms or views is recommended to be created on the 8i database so that I can fetch the data from tables on 7 database into the 9i database more quickly and efficiently.
Tom Kyte

Followup  

January 31, 2007 - 1:09 pm UTC

I would test 9iR2 to 7.3 before I'd use the man in the middle approach (it was 10g that 7.3 was kaput).

It is less a question of efficiency (views/synonyms) - a synonym has a slight advantage in the parse phase. A view would import the meta data into the other database (which a synonym would not) which has advantages as well in some cases.

so, use either one (or just skip the 8i instance if at all possible)

Database Link with VPD and Application Context

January 30, 2007 - 8:22 am UTC

Reviewer: Max

I'm facing strange problems with a certain type of insert via a public database link pointing from a local (9iR2 on WIN XP) to a remote database (9iR2 on AIX).

These inserts fail due to NO_DATA_FOUND exceptions within triggers on (remote) target tables.
The triggers do the following very simple lookup from a (remote) parent table before insert for each row:

select <MyCol1> into :NEW.<MyCol1>
from <MySchema>.<MyTab>
where <MyCol2> = :NEW.<MyCol2>
and <MyCol2> = :NEW.<MyCol3>

There are VPD policies in place for insert, update, delete, and select on both, source and target tables.
The database link uses a remote account with role DBA and additional "exempt access policy" system privilege.

It has been verified (by performing minus set operations) that both, local and remote parent table contain the same set of data.

<MySchema>.<MyTab>.<MyCol2> is feed via a column default which takes its value from an application context. It has been proven that this session context had been successfully initialized on the remote site from within the local site. The expected values could be read out from that context on the remote site from within the local site via the database link through dictionary views as well as with user-defined packaged functions. Furthermore a very similar insert accessing nothing but the local database (without a database link) succeeds and inserts rows that get a *NEW* value for <MySchema>.<MyTab>.<MyCol> (which is part of the primary key) taken from that session context. The only difference compared to the failing inserts using the database link is that the latter do NOT get a NEW value from the session context but the value that already exists within the local site (and is about to be copied to the remote site).

Can you imagine any reason(s) why such similar inserts via database link fail?

Tom Kyte

Followup  

January 31, 2007 - 12:37 pm UTC

insufficient data here - would need a test case to work with. sorry...

As for "Database Link with VPD and Application Context "

January 31, 2007 - 1:47 am UTC

Reviewer: Max

I've found a call to sys_context( 'userenv', 'os_user' ) inside a policy function to return a *different* value when called via the database link (even if this points back to the same database).

I'm not quite sure whether one should have expected such behaviour ...
Tom Kyte

Followup  

January 31, 2007 - 10:03 am UTC

the OS_USER on the dblink would be different - it is a different OS user doing the work here - it is a server to server conversation - not a client to server

sys_context via db link (cont.)

February 03, 2007 - 9:03 am UTC

Reviewer: Max

Hmmm, I'm not quite sure: Client and server reside on the same machine. I 've received my os-user's name in both cases but preceeded by domain(?) in one of them ...

Meanwhile I've opened a TAR (including the test case), but they haven't been able to reproduce the outcome so far ...

Performance related to db links

April 06, 2007 - 12:58 pm UTC

Reviewer: Vikas Khanna from INDIA

Hi Tom,

I am desparately looking help from you and hope you will do to get this resolved.

We have a statement given below which used to take about an hr to complete and insert data in the denormalized table. Howver we have moved the denorm table on another dastabase and using db link trying to insert the data using the same sql and it is taking too long a time to complete.

It has already passed 4 hrs and still running. I have choosen the push process to get the data pushed so that the parallel processes and the has joins should function the same way they used to do in the single instance, It is at the time of insert it should go for serial execution.

Explain plan for INSERT /*+ PARALLEL(imp_denorm 16) */ INTO imp_clk_invrep_denorm imp_denorm
(
request_tag,
impression_tag,
click_tag,
impression_timestamp,
click_timestamp,
invalid_click_report_timestamp,
invalid_imp_report_timestamp,
account_id,
ad_campaign_id,
ad_id,
ad_creative_id,
ad_match_id,
ad_match_bid_id,
ad_position,
--ad_count,
ad_cost,
imp_rank,
publisher_id,
treatment_id,
channel_id,
request_count,
report_date,
created_date,
updated_date,
invalid_click_filter_id,
invalid_imp_filter_id,
imp_upd_flag,
clk_upd_flag,
inv_imp_upd_flag,
inv_clk_upd_flag,
dup_imp_flag,
invalid_imp_data_score,
invalid_clk_data_score
)
(
SELECT /*+ ORDERED PARALLEL(req 16) PARALLEL(imp 16) PARALLEL(clk 16) USE_HASH(imp clk) USE_HASH(req) */
imp.request_tag,
imp.impression_tag,
clk.click_tag,
FROM_TZ(imp.impression_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles' AS impression_timestamp,
FROM_TZ(clk.click_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles' AS click_timestamp,
NULL invalid_click_report_timestamp,
NULL invalid_imp_report_timestamp,
imp.account_id,
imp.ad_campaign_id,
imp.ad_id,
imp.ad_creative_id,
imp.ad_match_id,
imp.ad_match_bid_id,
imp.ad_position,
--imp.ad_count,
imp.ad_cost,
NULL imp_rank,
req.publisher_id,
req.treatment_id,
req.channel_id,
req.request_count,
TRUNC(FROM_TZ(imp.impression_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles') report_date,
sysdate,
sysdate,
NULL invalid_click_filter_id,
NULL invalid_imp_filter_id,
1 imp_upd_flag,
(CASE WHEN click_tag IS NOT NULL THEN 1 ELSE NULL END) clk_upd_flag,
NULL inv_imp_upd_flag,
NULL inv_clk_upd_flag,
NULL dup_imp_flag,
NULL invalid_imp_data_score,
NULL invalid_clk_data_score
FROM
impression_data imp,
click_data clk,
request_data req
WHERE
imp.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND imp.insert_date <= to_date('24/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
req.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss')-1/24 AND req.insert_date <= to_date('24/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
clk.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND clk.insert_date <= to_date('24/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
imp.impression_tag = clk.impression_tag(+) AND
req.request_tag = imp.request_tag
UNION ALL
SELECT /*+ ORDERED PARALLEL(req 16) PARALLEL(imp 16) PARALLEL(clk 16) USE_HASH(clk imp) USE_HASH(req) */
imp.request_tag,
imp.impression_tag,
clk.click_tag,
FROM_TZ(imp.impression_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles' AS impression_timestamp,
FROM_TZ(clk.click_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles' AS click_timestamp,
NULL invalid_click_report_timestamp,
NULL invalid_imp_report_timestamp,
imp.account_id,
imp.ad_campaign_id,
imp.ad_id,
imp.ad_creative_id,
imp.ad_match_id,
imp.ad_match_bid_id,
imp.ad_position,
--imp.ad_count,
imp.ad_cost,
NULL imp_rank,
req.publisher_id,
req.treatment_id,
req.channel_id,
req.request_count,
TRUNC(FROM_TZ(imp.impression_timestamp,'UTC') AT TIME ZONE 'America/Los_angeles') report_date,
sysdate,
sysdate,
NULL invalid_click_filter_id,
NULL invalid_imp_filter_id,
1 imp_upd_flag,
(CASE WHEN click_tag IS NOT NULL THEN 1 ELSE NULL END) clk_upd_flag,
NULL inv_imp_upd_flag,
NULL inv_clk_upd_flag,
(CASE WHEN imp.insert_date <= to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') THEN 1 ELSE NULL END) dup_imp_flag,
NULL invalid_imp_data_score,
NULL invalid_clk_data_score
FROM
click_data clk ,impression_data imp, request_data req
WHERE
clk.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND clk.insert_date <= to_date('24/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
imp.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss')-4 AND imp.insert_date <= to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
req.insert_date > to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss')-4 AND req.insert_date <= to_date('23/03/2007 00:00:00','dd/mm/yyyy hh24:mi:ss') AND
imp.impression_tag = clk.impression_tag AND req.request_tag = imp.request_tag
);
dwuser@ADMW>select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 2794969881

------------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Pstart| Pstop | TQ |IN-OUT| PQ Distrib |
------------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | 13M| 2864M| | 216K (65)| 00:43:22 | | | | | |
| 1 | PX COORDINATOR | | | | | | | | | | | |
| 2 | PX SEND QC (RANDOM) | :TQ10007 | | | | | | | | Q1,07 | P->S | QC (RAND) |
| 3 | BUFFER SORT | | 1048M| 129G| | | | | | Q1,07 | PCWP | |
| 4 | UNION-ALL | | | | | | | | | Q1,07 | PCWP | |
|* 5 | HASH JOIN | | 2754K| 567M| 44M| 78347 (2)| 00:15:41 | | | Q1,07 | PCWP | |
| 6 | PX RECEIVE | | 4728K| 658M| | 34351 (2)| 00:06:53 | | | Q1,07 | PCWP | |
| 7 | PX SEND HASH | :TQ10003 | 4728K| 658M| | 34351 (2)| 00:06:53 | | | Q1,03 | P->P | HASH |
| 8 | BUFFER SORT | | 1048M| 129G| | | | | | Q1,03 | PCWP | |
|* 9 | HASH JOIN | | 4728K| 658M| 357M| 34351 (2)| 00:06:53 | | | Q1,03 | PCWP | |
| 10 | PX RECEIVE | | 55M| 5092M| | 16404 (4)| 00:03:17 | | | Q1,03 | PCWP | |
| 11 | PX SEND HASH | :TQ10000 | 55M| 5092M| | 16404 (4)| 00:03:17 | | | Q1,00 | P->P | HASH |
| 12 | PX BLOCK ITERATOR | | 55M| 5092M| | 16404 (4)| 00:03:17 | 11 | 12 | Q1,00 | PCWC | |
|* 13 | TABLE ACCESS FULL| IMPRESSION_DATA | 55M| 5092M| | 16404 (4)| 00:03:17 | 11 | 12 | Q1,00 | PCWP | |
| 14 | PX RECEIVE | | 40444 | 1935K| | 104 (0)| 00:00:02 | | | Q1,03 | PCWP | |
| 15 | PX SEND HASH | :TQ10001 | 40444 | 1935K| | 104 (0)| 00:00:02 | | | Q1,01 | P->P | HASH |
| 16 | PX BLOCK ITERATOR | | 40444 | 1935K| | 104 (0)| 00:00:02 | 11 | 12 | Q1,01 | PCWC | |
|* 17 | TABLE ACCESS FULL| CLICK_DATA | 40444 | 1935K| | 104 (0)| 00:00:02 | 11 | 12 | Q1,01 | PCWP | |
| 18 | PX RECEIVE | | 31M| 2104M| | 34066 (2)| 00:06:49 | | | Q1,07 | PCWP | |
| 19 | PX SEND HASH | :TQ10004 | 31M| 2104M| | 34066 (2)| 00:06:49 | | | Q1,04 | P->P | HASH |
| 20 | PX BLOCK ITERATOR | | 31M| 2104M| | 34066 (2)| 00:06:49 | 10 | 12 | Q1,04 | PCWC | |
|* 21 | TABLE ACCESS FULL | REQUEST_DATA | 31M| 2104M| | 34066 (2)| 00:06:49 | 10 | 12 | Q1,04 | PCWP | |
|* 22 | HASH JOIN | | 11M| 2296M| 178M| 138K (3)| 00:27:42 | | | Q1,07 | PCWP | |
| 23 | PX RECEIVE | | 18M| 2631M| | 44835 (4)| 00:08:59 | | | Q1,07 | PCWP | |
| 24 | PX SEND HASH | :TQ10005 | 18M| 2631M| | 44835 (4)| 00:08:59 | | | Q1,05 | P->P | HASH |
|* 25 | HASH JOIN | | 18M| 2631M| | 44835 (4)| 00:08:59 | | | Q1,05 | PCWP | |
| 26 | PX RECEIVE | | 40444 | 1935K| | 104 (0)| 00:00:02 | | | Q1,05 | PCWP | |
| 27 | PX SEND BROADCAST | :TQ10002 | 40444 | 1935K| | 104 (0)| 00:00:02 | | | Q1,02 | P->P | BROADCAST |
| 28 | PX BLOCK ITERATOR | | 40444 | 1935K| | 104 (0)| 00:00:02 | 11 | 12 | Q1,02 | PCWC | |
|* 29 | TABLE ACCESS FULL | CLICK_DATA | 40444 | 1935K| | 104 (0)| 00:00:02 | 11 | 12 | Q1,02 | PCWP | |
| 30 | PX BLOCK ITERATOR | | 220M| 19G| | 44511 (4)| 00:08:55 | 7 | 11 | Q1,05 | PCWC | |
|* 31 | TABLE ACCESS FULL | IMPRESSION_DATA | 220M| 19G| | 44511 (4)| 00:08:55 | 7 | 11 | Q1,05 | PCWP | |
| 32 | PX RECEIVE | | 121M| 8077M| | 55154 (2)| 00:11:02 | | | Q1,07 | PCWP | |
| 33 | PX SEND HASH | :TQ10006 | 121M| 8077M| | 55154 (2)| 00:11:02 | | | Q1,06 | P->P | HASH |
| 34 | PX BLOCK ITERATOR | | 121M| 8077M| | 55154 (2)| 00:11:02 | 7 | 11 | Q1,06 | PCWC | |
|* 35 | TABLE ACCESS FULL | REQUEST_DATA | 121M| 8077M| | 55154 (2)| 00:11:02 | 7 | 11 | Q1,06 | PCWP | |
------------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

5 - access("REQ"."REQUEST_TAG"="IMP"."REQUEST_TAG")
9 - access("IMP"."IMPRESSION_TAG"="CLK"."IMPRESSION_TAG")
13 - filter("IMP"."INSERT_DATE"<=TO_DATE('2007-03-24 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "IMP"."INSERT_DATE">TO_DATE('2007-03-23
00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
17 - filter("CLK"."INSERT_DATE"<=TO_DATE('2007-03-24 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "CLK"."INSERT_DATE">TO_DATE('2007-03-23
00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
21 - filter("REQ"."INSERT_DATE"<=TO_DATE('2007-03-24 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "REQ"."INSERT_DATE">TO_DATE('2007-03-22
23:00:00', 'yyyy-mm-dd hh24:mi:ss'))
22 - access("REQ"."REQUEST_TAG"="IMP"."REQUEST_TAG")
25 - access("IMP"."IMPRESSION_TAG"="CLK"."IMPRESSION_TAG")
29 - filter("CLK"."INSERT_DATE"<=TO_DATE('2007-03-24 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "CLK"."INSERT_DATE">TO_DATE('2007-03-23
00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
31 - filter("IMP"."INSERT_DATE"<=TO_DATE('2007-03-23 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "IMP"."INSERT_DATE">TO_DATE('2007-03-19
00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
35 - filter("REQ"."INSERT_DATE"<=TO_DATE('2007-03-23 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND "REQ"."INSERT_DATE">TO_DATE('2007-03-19
00:00:00', 'yyyy-mm-dd hh24:mi:ss'))

62 rows selected.

However when using the db-link wadm.amazon it gives me a horrible plan
dwuser@ADMW>select * from table(dbms_xplan.display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Plan hash value: 660507896

-------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Inst |IN-OUT|
-------------------------------------------------------------------------------------------------------
| 0 | INSERT STATEMENT REMOTE| | 13M| 2731M| | 15M (52)| 50:39:17 | |
| 1 | UNION-ALL | | | | | | | |
|* 2 | HASH JOIN | | 2754K| 541M| 662M| 7512K (3)| 25:02:34 | |
|* 3 | HASH JOIN | | 4728K| 608M| 5722M| 3470K (4)| 11:34:12 | |
| 4 | REMOTE | | 55M| 5092M| | 3164K (4)| 10:32:59 | ! |
| 5 | REMOTE | | 40444 | 1500K| | 20628 (2)| 00:04:08 | ! |
| 6 | REMOTE | | 31M| 2134M| | 3883K (3)| 12:56:48 | ! |
|* 7 | HASH JOIN | | 11M| 2190M| 2649M| 7683K (3)| 25:36:43 | |
|* 8 | FILTER | | 40444 | 1500K| | 20628 (2)| 00:04:08 | |
| 9 | REMOTE | | | | | | | ! |
| 10 | REMOTE | | 121M| 8193M| | 3883K (3)| 12:56:45 | ! |
-------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("A6"."REQUEST_TAG"="A8"."REQUEST_TAG")
3 - access("A8"."IMPRESSION_TAG"="A7"."IMPRESSION_TAG")
7 - access("A3"."REQUEST_TAG"="A4"."REQUEST_TAG")
8 - filter("A5"."INSERT_DATE">TO_DATE('2007-03-23 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND
"A5"."INSERT_DATE"<=TO_DATE('2007-03-24 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND
"A4"."INSERT_DATE">TO_DATE('2007-03-19 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND
"A4"."INSERT_DATE"<=TO_DATE('2007-03-23 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))

Note
-----
- fully remote statement

My observations:

1. When doing a hash join it is dumping the table contents to the temp tablespace and then when viewed from the V$session_longops the time remaining for the HASH JOIN being done by parallel slaves keeps on increasing and the IO Wait just goes to Zero with 99% CPU shown in the idle state.

Hash joins as always were noticed extremely slow as compared on a daily basis. the same HASH join would get completed in 10 mins was showing a time of 48769 secs to complete for each parallel slave, There was no other activity on the database server.

Since everything till insert is performed locally WHY has joins have become extremely slow.

What can be done to improve its performace,

Thanks a lot in advance.

Tom Kyte

Followup  

April 09, 2007 - 10:12 am UTC

this used to be a parallel direct path insert, it isn't when you introduced the dblink. It isn't that the hash join is "slower" probably, it is that the thing that fed off of the hash join (the insert) is

a) working over a dblink - not process to process local communication (network = not as fast)

b) not direct path anymore

c) not in parallel



April 25, 2007 - 4:44 pm UTC

Reviewer: Alexander the ok

Hi Tom,

I need some ideas from you please for the following problem, we are out. We are using streams to keep a schema in sync between two sites. Unfortunately streams bombs often enough that we need a way to sync them back up again. I can use a merge over a db link that works beautifully however we have one table with CLOBs.

Since these are active sites, the only way I can think of to do this to shut them down and use imp/exp. What do you think? Are we out of luck? Thank you.

Who's using db link

May 07, 2007 - 1:37 pm UTC

Reviewer: Dan from PA, USA

Hi Tom,

Is there way to know who's using a db link? Say, after a user issued two queries like "select sysdate from dual@db1" and "selet sysdate from daul@db2", Oracle kept the both link "session" open. How can we find out the user has these two "link sessions" open?

Thank you!


end-of-file on communication channel

June 11, 2007 - 12:48 am UTC

Reviewer: mohammed from qatar

Hi Tom,

i have two database connected to each other but always im getting error
Errors in file /u01/app/oracle9i/admin/PROD/udump/prod1_reco_674046.trc:
ORA-02068: following severe error from CEN_LINK
ORA-03113: end-of-file on communication channel

but im lucky because still its working again it seems the connection get disconnect and connect again automatically

Thanks Alot

June 13, 2007 - 5:58 am UTC

Reviewer: A reader

ORA-02068: following severe error from CEN_LINK
ORA-03113: end-of-file on communication channel

Tom Kyte

Followup  

June 13, 2007 - 8:15 am UTC

ora-3113, ora-600, ora-7445 => support.

OK

July 20, 2007 - 12:57 am UTC

Reviewer: Kumar

Hi Tom,
When we use a Database Link to connect to a remote database,
Does it create a session in Target database?
If not,In target databases how we can identify the sessions that have connected remotely?
Thanks for your time.
Tom Kyte

Followup  

July 20, 2007 - 8:16 am UTC

yes, it creates a session.

monitor the db link

July 26, 2007 - 4:20 am UTC

Reviewer: Daniel from CZE

hi tom, is it possible to monitor if the db link is currently ok?
can you help me to find the best solution how to do that?

thanks
daniel

Tom Kyte

Followup  

July 27, 2007 - 8:26 am UTC

define "ok"

Authentication for fixed user database link

August 08, 2007 - 11:30 am UTC

Reviewer: Raza from Canada

Hi Tom,

Can you please explain, how the authentication for fixed user database link occurs. More precisely I am interested in knowing if the userid and password are sent in clear text over the network ?

I would appreciate if you point me out to any documentation that talks about this in detail.

Thanks

Tom Kyte

Followup  

August 14, 2007 - 10:14 am UTC

passwords are not sent in the clear over the network

and if you use ASO (advanced security) all network traffic may be encrypted if you wish.

passwords have been encrypted by the transmitting client for a decade or more...

Create Db link with as sysdba for sys user in standby db

August 09, 2007 - 4:22 pm UTC

Reviewer: A reader

Hi, DB verion 9208
How do I create a Database link to connect to sys as sysdba to a remote db.

create database link connect to "sys as sysdba" identified
by password using 'host'

I tried this. Link gets created but it gives error
oracle inittialization or shutdown in progress.

I am trying to connect to a stand by DB. I believe for a Standby DB , only connections as sysdba are permitted hence the above error.

If I use sqlplus and directly connect sys as sysdba it works fine.
How to get the link working ?

Info across Db-links

August 10, 2007 - 8:00 am UTC

Reviewer: martina from vienna, austria

Hi Tom,

What possibility do we have to get information across db-links? something like dbms_application_info.set_client_info (did not work). can i find out something with sys_context? Too many people (not users, not os-users) are retrieving using db_links and thus we would like to use any Info with FGAC at the remote site. i would also be thankful for some documentation-link for me to read!

thank you in advance!

martina
Tom Kyte

Followup  

August 14, 2007 - 11:00 am UTC

the remote database would be reliant on the local database to have SENT this information over the link. The local database that opens the connection should invoke dbms_application_info@remote_site in order to set these values.

Info across DB-Link

August 14, 2007 - 11:37 am UTC

Reviewer: martina from vienna, austria

Thank you, that works great!

Do you have an idea how i could automate this thing - something like a "before_opening_db_link"-trigger?

thanks,

martina
Tom Kyte

Followup  

August 20, 2007 - 12:05 pm UTC

stored procedures :)

there is no such a triggering event - your local session would need to invoke something.

About remote connection to Database

August 15, 2007 - 1:16 pm UTC

Reviewer: xgla from USA

Hi Tom, your followup are very usuful for me.
I have a problem. I want to connect my DB from a remote pc in other network.
I install Net Service and I configured my tnsname.ora.
I put in host name my static Ip where is open the port 1521 in my server. But I get the error
TNS-12535 - TNS- Operation time out.
My server is dedicated, I have only one listener, one database. I traced my listener in the server and the conecctin is establish, and I treced the cliente too, I got the tns-12535, 12560, 505, and 60 error.
My question is :
There are other parameter that I have configurated in order to connect my DB remotely ?
Thank in advanced.
Tom Kyte

Followup  

August 20, 2007 - 7:19 pm UTC

would there happen to be a big old firewall in the way

About remote connection to Database

August 28, 2007 - 9:42 am UTC

Reviewer: xgla from USA

Yes, I have a good firewall, a watchguard firebox, but I have open the 1521 port. I noted that listener give other random port to process.
How to do in this case ?
Thank you so much.
Tom Kyte

Followup  

September 04, 2007 - 1:43 pm UTC

tell us more about how you currently have this database setup, are you trying to use shared server? what operating system.


pass login/password while invoking dblink?

September 19, 2007 - 4:09 am UTC

Reviewer: nairs

If I create a db link without the connect to clause (create database link db1 using 'mydb';) and if the user on the linked target database is different from the one on the source database, it gives the invalid username/password error.

Apart from modifying the db link name with 'connect to..identified by..', is there a way to give the username and password while invoking the dblink? (something like select * from dual@db1@user/pwd?)
Tom Kyte

Followup  

September 19, 2007 - 12:38 pm UTC

no, there is not.

DB Links

October 23, 2007 - 2:12 pm UTC

Reviewer: Rajesh from Hartford,CT

Hi Tom,

I have a problem in DB Links. I have 2 databases A and B.
Both are linked each other by DB Links. In A, we have two schemas S1 and S2. A procedure in S1 updates a table in S2.
Grants,synonyms and everything are all good between S1 and S2. Now if we call the procedure in A from database B, I get Invalid Username/Password showing the error in the update statement.

If the table is in the same schema S1, it works.
If the table is in S2 schema, it doesnt work.

The DB link is created between A and B through S1. Should I have to create another DB Link between A and B through S2 ?

Can you help me in this ?

Thanks
Rajesh
Tom Kyte

Followup  

October 23, 2007 - 6:44 pm UTC

how could a STORED PROCEDURE call give an "update error"

you have not described this very well.

there is nothing to comment on.

DB Links

October 23, 2007 - 8:18 pm UTC

Reviewer: Rajesh from Hartford,CT

Hi Tom,

When the procedure is invoked from the different database B, the statements within the proc starts executing and when the update stmt on a table of another schema is executed, I get the error.

It may be because of when an another schema's (S2 of same database A) table is to be updated, it requires the username/password to execute the update from a different database B though it has a DB link with database A (with schema S1).

Should I also create a similar DB link (like database B and schema S1 of A) for database B along with the schema S2 of database A which has the table ?

Thanks
Rajesh
Tom Kyte

Followup  

October 24, 2007 - 8:54 am UTC

without an example, without the ACTUAL ERROR MESSAGE, I cannot comment.

It should not matter if the code is executed via a dblink.

ORA-02064

October 24, 2007 - 4:05 pm UTC

Reviewer: Anne from MN, USA

Hi Tom,

I have 2 databases A and B. A is 9.2.0.4 and B is 11i Ebiz 9.2.0.6 RDBMS.

Package in A calls package in B (which has out and commit) over a dblink => I get 02064 error.

I am not sure how to resolve this, because I cannot take the commit out of pkg in B.

Basically what pkg in A does is calculates billable dollars in A and creates invoices in B :
1. Does a bunch of calculations to create Invoices for billable projects
2. Inserts into tables in A
3. Inserts into staging tables in B
4. Commit in A (so data is committed in B from step 3)
5. Calls create_11i_invoice@B to create invoices from the staging tables in B. create_11i_invoice is a generic pkg in B that creates invoices using the 11i api's, so I cannot take off the commits from there.

Could you please advise on how I could do this ? Thanks so much and appreciate your help!
Tom Kyte

Followup  

October 24, 2007 - 4:19 pm UTC

you cannot do transactional control over a dblink - the remote site isn't allowed to commit (the invoking site has to sort of make that decision, they are the only one that knows what all is involved in actually committing - it could be many other sites - that one remote site has no clue)

you'll need to change the process - perhaps you schedule a JOB in "b" and when you call dbms_job@remote and schedule and commit it - it'll run FROM b shortly after.

and then B is the "coordinating site" and B can commit

ORA-02064

October 24, 2007 - 4:58 pm UTC

Reviewer: Anne from MN, USA

Thanks so much, Tom, excellent idea!

Couple of questions :
1. In "B", job_queue_processes = 10.job_queue_interval is not set. Is this ok for dbms_job to function ?

2. Schedule a job in B :
procedure schedule_job_create_inv
as
  l_job   number;
  l_errbuf          varchar2(100);
  l_retcode         number;
  g_org_id        number := 108;
begin
   dbms_job.submit(l_job, 'apps.create_11i_invoice_pkg.create_11i_invoice(l_errbuf, l_retcode, g_org_id);');
end;
/

Could you please confirm if the above is correct ?

3. Call dbms_job@remote and schedule and commit
In pkg :
dbms_job.run(job_number)@B;
commit;


I am not sure if this is correct. Please advise.

Once again thanks so much for your help. Much appreciated and very valuable!

Tom Kyte

Followup  

October 25, 2007 - 5:47 pm UTC

1) job queue interval is a hidden parameter these days, do not set it.
2) you'd want to run that block of code ON B, yes. Either by calling dbms_job@remote or by having this procedure schedule job create inv residing on B

3) no, you submit the job remotely. When you COMMIT, it runs - on B - not distributed - and can commit.

it looks like you have "in out parameters" to your procedure (your job), that won't work. especially the OUT parameters

we are queueing a job to be executed - after we commit - in some other session. You'll use a table to get inputs/outputs to and from this job.

Not sure that I understand

October 26, 2007 - 11:12 am UTC

Reviewer: Anne from MN, USA

Thanks so much, Tom, but I am not sure that I understand this completely...
Could you please help and thanks for your patience...

From what I understand, I have to create this proc sched_create_inv on B.
Then on A, call sched_create_inv@remoteB and commit in A => This will run the proc sched_create_inv on B and in turn run the create_11i_pkg on B.
Am I following you so far ?

I lost you completely on "You'll use a table to get inputs/outputs to and from this job"... Could you help.

Thanks so much.

Tom Kyte

Followup  

October 29, 2007 - 11:23 am UTC

a) this stuff would exist on "B"


create table create_inv_parameters( job number primary key, errm varchar2(100), retcode number, org_id number );

procedure schedule_job_create_inv( p_org_id in number )
as
  l_job   number;
begin
  dbms_job.submit(l_job,'apps.create_11i_invoice_pkg.create_11i_invoice(JOB);');
  insert into create_inv_parameters( job, org_id ) values ( l_job, p_org_id );
end;
/



Your procedure create_11i_invoice would start with:
.... ( p_job in number ) /* only parameter, the JOB ID */
as
  ...
  l_rec create_inv_parameters%rowtype;
begin
  select * into l_rec from create_inv_parameters where job = p_job;

  .... process, l_rec.org_id has your org id

  update create_inv_parameters set errm = l_errm,  retcode = l_retcode
  where job = p_job;
end;
/



b) from A, you call

schedule_job_create_inv@B( l_org_id );
commit; <<== that permits the job to run asynchronously on the remote site

c) later, you can query create_inv_parameters@b to see how the job did


dbms_job

October 30, 2007 - 4:54 pm UTC

Reviewer: Anne from MN, USA

Thank you so much Tom - that was extrememly helpful - it works great!

Database link in cursor

November 22, 2007 - 3:57 pm UTC

Reviewer: Czesiu from POLAND

Hi Tom,
I try to get user table names from remote database and then question them about number of rows, so I use:

DECLARE
counter NUMBER;
sql_stmt VARCHAR2(500);
CURSOR tables IS
SELECT table_name FROM user_tables@SVT;
BEGIN
FOR tab IN tables LOOP
sql_stmt := 'SELECT COUNT(*) FROM '||tab.table_name||'@SVT';
EXECUTE IMMEDIATE (sql_stmt) INTO counter;
DBMS_OUTPUT.PUT_LINE(tab.table_name||' '||counter);
END LOOP;
END;

All the time I encounter ORA-00903 error: 'Invalid table name'. Did i make any mistake? Isn't that Pl/SQL code valid?

Thanks & Regards


Tom Kyte

Followup  

November 26, 2007 - 11:16 am UTC

why not just:

select table_name, num_rows from user_tables@svt;

presuming of course that they have valid statistics, it would give you a good guesstimate.


ops$tkyte%ORA10GR2> DECLARE
  2    counter NUMBER;
  3    sql_stmt VARCHAR2(500);
  4    CURSOR tables IS
  5       SELECT table_name FROM user_tables@ora10gr2@loopback;
  6  BEGIN
  7    FOR tab IN tables LOOP
  8      sql_stmt := 'SELECT COUNT(*) FROM '||tab.table_name||'@ora10gr2@loopback';
  9      EXECUTE IMMEDIATE (sql_stmt) INTO counter;
 10      DBMS_OUTPUT.PUT_LINE(tab.table_name||' '||counter);
 11  END LOOP;
 12  END;
 13  /
T_HEAP 10000
T 50301
TEST2 3
TEST1 5
T1 35
EMP 2
T2 35
T_HASH 10000

PL/SQL procedure successfully completed.


code does "function" however - maybe you want to try once:

ops$tkyte%ORA10GR2> DECLARE
  2    counter NUMBER;
  3    sql_stmt VARCHAR2(500);
  4    CURSOR tables IS
  5       SELECT table_name FROM user_tables@ora10gr2@loopback;
  6  BEGIN
  7    FOR tab IN tables LOOP
  8      sql_stmt := 'SELECT COUNT(*) FROM '||tab.table_name||'@ora10gr2@loopback';
  9      DBMS_OUTPUT.PUT_LINE(sql_stmt);
 10      EXECUTE IMMEDIATE (sql_stmt) INTO counter;
 11      DBMS_OUTPUT.PUT_LINE(tab.table_name||' '||counter);
 12  END LOOP;
 13  END;
 14  /
SELECT COUNT(*) FROM T_HEAP@ora10gr2@loopback
T_HEAP 10000
SELECT COUNT(*) FROM T@ora10gr2@loopback
T 50301
SELECT COUNT(*) FROM TEST2@ora10gr2@loopback
TEST2 3
SELECT COUNT(*) FROM TEST1@ora10gr2@loopback
TEST1 5
SELECT COUNT(*) FROM T1@ora10gr2@loopback
T1 35
SELECT COUNT(*) FROM EMP@ora10gr2@loopback
EMP 2
SELECT COUNT(*) FROM T2@ora10gr2@loopback
T2 35
SELECT COUNT(*) FROM T_HASH@ora10gr2@loopback
T_HASH 10000

PL/SQL procedure successfully completed.


and what you see might become "obvious" - eg: I can make this break easily:

ops$tkyte%ORA10GR2> create table "hahahahaha" (x int);

Table created.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> DECLARE
  2    counter NUMBER;
  3    sql_stmt VARCHAR2(500);
  4    CURSOR tables IS
  5       SELECT table_name FROM user_tables@ora10gr2@loopback;
  6  BEGIN
  7    FOR tab IN tables LOOP
  8      sql_stmt := 'SELECT COUNT(*) FROM '||tab.table_name||'@ora10gr2@loopback';
  9      DBMS_OUTPUT.PUT_LINE(sql_stmt);
 10      EXECUTE IMMEDIATE (sql_stmt) INTO counter;
 11      DBMS_OUTPUT.PUT_LINE(tab.table_name||' '||counter);
 12  END LOOP;
 13  END;
 14  /
SELECT COUNT(*) FROM hahahahaha@ora10gr2@loopback
DECLARE
*
ERROR at line 1:
ORA-00942: table or view does not exist
ORA-02063: preceding line from ORA10GR2@LOOPBACK
ORA-06512: at line 10



which would be corrected by doing this:

ops$tkyte%ORA10GR2> DECLARE
  2    counter NUMBER;
  3    sql_stmt VARCHAR2(500);
  4    CURSOR tables IS
  5       SELECT '"' || table_name || '"' table_name FROM user_tables@ora10gr2@loopback;
  6  BEGIN
  7    FOR tab IN tables LOOP
  8      sql_stmt := 'SELECT COUNT(*) FROM '||tab.table_name||'@ora10gr2@loopback';
  9      DBMS_OUTPUT.PUT_LINE(sql_stmt);
 10      EXECUTE IMMEDIATE (sql_stmt) INTO counter;
 11      DBMS_OUTPUT.PUT_LINE(tab.table_name||' '||counter);
 12  END LOOP;
 13  END;
 14  /
SELECT COUNT(*) FROM "hahahahaha"@ora10gr2@loopback
"hahahahaha" 0
SELECT COUNT(*) FROM "T_HEAP"@ora10gr2@loopback
"T_HEAP" 10000
SELECT COUNT(*) FROM "T"@ora10gr2@loopback
"T" 50301
SELECT COUNT(*) FROM "TEST2"@ora10gr2@loopback
"TEST2" 3
SELECT COUNT(*) FROM "TEST1"@ora10gr2@loopback
"TEST1" 5
SELECT COUNT(*) FROM "t"@ora10gr2@loopback
"t" 0
SELECT COUNT(*) FROM "T1"@ora10gr2@loopback
"T1" 35
SELECT COUNT(*) FROM "EMP"@ora10gr2@loopback
"EMP" 2
SELECT COUNT(*) FROM "T2"@ora10gr2@loopback
"T2" 35
SELECT COUNT(*) FROM "T_HASH"@ora10gr2@loopback
"T_HASH" 10000

PL/SQL procedure successfully completed.

database links

November 24, 2007 - 3:19 am UTC

Reviewer: A reader

hai tom,

How can i see the changes in remote database table after the trigger is fired in a local database?.i could see the changes in local database ,but not on remote database...
here is the example wat i have did..

1) ::TO CREATE A DATABASE LINK IN SCOTT,N CREATING LINK TO WB(ANOTHERDATABASE)::

create database link dblinkwbh
connect to WB
identified by wb
using 'WB';

Database link created.

2)THEN I HAVE CREATED A TRIGGER IN SCOTT FOR INSERTING :
CREATE OR REPLACE TRIGGER TG_AFTER_INSERT
AFTER INSERT
ON test_dblink
REFERENCING OLD AS OLD NEW AS NEW
FOR EACH ROW
BEGIN
pro_test1(:new.bacno,:new.name);
end;
/
TRIGGER CREATED .
create or replace procedure pro_test1(p_bacno number,p_name varchar2)
as
begin
insert into wbh@dblinkwbh(mem_bacno,mem_name)
values(p_bacno,p_name);
exception when others then Rollback;
commit;
end;

PROCEDURE CREATED.

3)WHEN I INSERT DATA IN TABLE test_dblink ... THE TRIGGER IS FIRED N PROCEDURE IS ALSO EXECUTED..AND I CAN SEE THE CHANGES IN LOCAL DATABASE ..
SELECT * FROM wbh@dblinkwbh;--COUNT IS INCREASED..

BUT WHEN I CONNECT TO WB DATABASE ..
I CANNOT SEE THE CHANGES IN WBH TABLE..
SELECT * FROM WBH;--NO CHANGES..I HAVE COMMITED IN THE DATABASE ALSO ..I CANT SEE THE CHANGES

CAN I KNOW THE REASON Y ???
THANKQ IN ADVANCE TOM





Tom Kyte

Followup  

November 26, 2007 - 11:54 am UTC

...
create or replace procedure pro_test1(p_bacno number,p_name varchar2)
as
begin
insert into wbh@dblinkwbh(mem_bacno,mem_name)
values(p_bacno,p_name);
exception when others then Rollback;
commit;
end;
...


good gosh - do you know what that does? that exception block??????????

ARG, I'm starting to give up.

If you hit any error, then - you silently rollback (which fortunately will fail since you are in a trigger anyway). You SILENTLY rollback. You SILENTLY AND IN AN UNDETECTABLE FASHION rollback. And then you commit. (that commit is part of the exception block)

It gets frustrating look at 'error handling' code that does so much serious damage like this.





so, the reason you cannot 'see' your changes should be obvious.


You create a new session on the remote site, it is not visible to that session until YOU COMMIT.

and the commit does not, will not, cannot be in the procedure.




Please - I suggest you look at every single exception block in your code and if you have any that

a) rolllback
b) commit

have someone that really knows what transactions are/mean look at your code.


also, if you have ANY instances of:

when others
then .....


and there IS NOT a "raise" or "raise_application_error" there - comment them out - they are the most dangerous bits of code. They must be removed.

committing updates over a link

December 07, 2007 - 8:45 am UTC

Reviewer: Dave Martin from The Hague, Holland

Tom,
are..

update blah@yyyy set xxx='fgh';
commit;

..and..

call update_blah@yyy('fgh');
commit;

..the same, assuming update_blah is a procedure on the remote database which simply updates blah and exits without a commit?

Recommended Uses for DB Links

December 10, 2007 - 12:59 pm UTC

Reviewer: Steve Landy from East Hartford, CT

Tom,

Regarding DB Links, we have a fairly diverse shared database environment existing between 4 different data centers in 4 different locations (2 of which are out of state). Quite frequently we get requests for DB Links to be setup between databases to pass data around (mostly batch type of jobs that run daily). Do you have any other recommended alternatives other than DB Links to serve the same type of purpose. We would like to keep the dependancy between databases limited (especially across the WAN). Any suggestions would be greatly appreciated. Also, what would you recommend as "best practices" for DB Links?
Tom Kyte

Followup  

December 10, 2007 - 1:53 pm UTC

Well, database links are the easiest way for a plsql routine to reach out and get data from another database.

how does it make a database "dependent" on another database? I can see how it makes a PROCESS dependent on two databases - but the databases themselves don't really care or use the dblinks?

Recommended Uses for DB Links

December 10, 2007 - 3:45 pm UTC

Reviewer: Steve Landy from East Hartford, CT

Well in that case it becomes a supportability/maintainability concern. If one DB needs to be taken down/upgraded/etc. and another DB has a DB Link association with that DB process (251 DBs in our environment) it becomes a maintenance nightmare to coordinate application teams and so forth to make sure there aren't any processes consuming data from the DB being maintenanced. We just recently got a request to have DB Links setup from one 1 Devel DB to 8 Prod DBs. In your, opinion do you think this is a moot point and isn't a concern from a supportability/maintainability standpoint? Would you recommend using DB Links as the "best practice" medium for exchanging data between disparate databases as apposed to other alternatives (especially across the WAN)?
Tom Kyte

Followup  

December 10, 2007 - 4:24 pm UTC

that will be true regardless of what "technology" you use.

period. remove the database link, introduce "X".

when the database isn't up, it cannot produce "X"
when the database isn't up, it cannot consume "X"

I don't care what integration technique you use - you have 251 points of conversation. Say you introduce some middleware, now you have way more than 251 points of conversation.

What I would focus on is getting from 251 database instance to - less.


Now that said, a development database should not have links to production - that just isn't smart.

Production to production - sure.

to development from production? *maybe* (because production is very controlled)

from development to production? I hesitate to say "never", but "pretty much never".


January 04, 2008 - 5:34 pm UTC

Reviewer: A reader

We have two databases A and B (version 9.0.2) running on different unix machines.

There is a database link created on A to refer tables in B.

Our front end application which is connected to A, reports error for database link with message code e.g. "PLS-00907 cannot load library unit ", but when we try to look into database error logs, we don't see any error logged.

Is there a way to find out whether the issue is with Database link or with Unix box and networking ?
Tom Kyte

Followup  

January 04, 2008 - 5:39 pm UTC

it won't be the unix box or networking - I cannot think of a single reason why it would be.

a pls error like that would not be "logged" anywhere - the application would get it and deal with it.

Now, you should be able to remove your application from the equation (just log into sqlplus and do the same thing - it should reproduce)

and from there, we'll want to whittle down the remote procedure to the smallest thing it can be in order to reproduce...

January 07, 2008 - 5:29 pm UTC

Reviewer: A reader

Hi Tom,

Thanks for information on PLS error logging.

To reproduce the error, as you mentioned, We took one of the SQL statement which refers to remote database out and ran it couple of time, but it did not error out.
We checked the application log and found that it is happening some random time. To mimic the way application being use, we ran the single SQL from sql plus through a loop for full day, but could not reproduce it.

Tom Kyte

Followup  

January 07, 2008 - 5:37 pm UTC

you'll want to utilize support - they can set an event that can capture additional information when the error occurs.

January 08, 2008 - 5:00 pm UTC

Reviewer: A reader

Thanks Tom.

We will do as you said and try to find some more information.

get data from 11g in 10g through db link

January 11, 2008 - 4:08 pm UTC

Reviewer: Sean from NJ, USA

Hi Tom,

I am not able to get data from 11g through 10g (10.2.0.3) database by using db link.  Here is the screen shot.  Is this the known behavior?  Thanks so much.  -- Sean

SQL> create database link nd30 connect to fdw identified by nd30 using 'nd30';

Database link created.

SQL> select sysdate from dual@nd30;
select sysdate from dual@nd30
                         *
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from ND30
SQL> connect fdw/nd30@nd30
Connected.

connect to 11g from 10 through db link

January 16, 2008 - 11:56 am UTC

Reviewer: sean from NJ, USA

Hi Tom,

Oracle support helped me solve the problem. In 11g, password is case sensitive, one needs to create db link like this:
create database link db11g connect to scott identified by "tiger" using 'db11g';

Thanks. -- Sean

password for db links

January 22, 2008 - 4:56 am UTC

Reviewer: Satya Prasad Moparthy from Bangalore

Hi Tom,
We have upgraded our databases to 8.1 to 10.2, and i used to refer sys.link$ view to check for the passwords of all the db links. But, i observed that this view does not contain the passwords anymore, where i can get the passwords for the db links and why it was removed from link$ view in version 10.
Tom Kyte

Followup  

January 22, 2008 - 7:24 am UTC

you won't.

that was the point of removing them.

and reason 21143242 why you should not query sys.* tables directly, they are ours and subject to massive change without warning.

dblink not working from stored procedure

February 12, 2008 - 8:41 pm UTC

Reviewer: Carlos from Bellevue, WA

Hi Tom,

Why is that a dblink works fine in independent queries but when I take the exact same query to create a cursor inside a procedure, I get the msg: "table or view not found". Thanks
Tom Kyte

Followup  

February 13, 2008 - 12:59 pm UTC

you ask if you can bind the order by ordinal - answer is NO, you cannot

but your example, which you seem to think is using a bind for that, is NOT using a bind.. You are using concatenation.

scott@test>create or replace procedure myproc (x out sys_refcursor,dep
tno int,y int default 1)
  2  as
  3  begin
  4  open x for 'Select * from emp where deptno = :dno <b>order by '||y </b> using 
deptn
o;
  5  end;
  6  /



you build a query like:

select * from emp where deptno = :dno order by 1



and then bind in the :dno, but not the ordinal.

Right Answer to Wrong Question?

February 13, 2008 - 1:29 pm UTC

Reviewer: Greg from Reston (you know where that is)

Tom, I think that you were answering *this* question:
using by bind in order by condition February 12, 2008 - 10pm US/Eastern

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:2320123769177#664602900346116237


Sorry but my question was other...

February 13, 2008 - 7:45 pm UTC

Reviewer: Carlos from Seattle, USA

Here goes again Tom:

Why is that a dblink works fine in independent queries but when I take the exact same query to create a cursor inside a procedure, I get the msg: "table or view not found". Thanks

Tom Kyte

Followup  

February 13, 2008 - 11:08 pm UTC

give me an example, tell us how the dblink is created (i'm guessing you do not have the user/pass in it, and when the procedure is run, it uses the credentials of the currently logged in user)

In order to answer you - we need *details*

an example would rock...

for example, consider what happens to scott, depending on how dblink is created:

ops$tkyte%ORA10GR2> create user a identified by a default tablespace users quota unlimited on users;

User created.

ops$tkyte%ORA10GR2> create user b identified by b;

User created.

ops$tkyte%ORA10GR2> grant create session, create table to a;

Grant succeeded.

ops$tkyte%ORA10GR2> grant create session, create procedure, create database link to b;

Grant succeeded.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> connect a/a
Connected.
a%ORA10GR2> create table t as select * from dual;

Table created.

a%ORA10GR2> grant select on t to b;

Grant succeeded.

a%ORA10GR2>
a%ORA10GR2> connect b/b
Connected.
b%ORA10GR2> create database link ora10gr2@loopback using 'ora10gr2';

Database link created.

b%ORA10GR2> select * from a.t@ora10gr2@loopback;

D
-
X

b%ORA10GR2> begin
  2          for x in (select * from a.t@ora10gr2@loopback)
  3          loop
  4                  null;
  5          end loop;
  6  end;
  7  /

PL/SQL procedure successfully completed.

b%ORA10GR2> create or replace procedure p
  2  as
  3  begin
  4          for x in (select * from a.t@ora10gr2@loopback)
  5          loop
  6                  dbms_output.put_line( 'row = ' || x.dummy );
  7          end loop;
  8  end;
  9  /

Procedure created.

b%ORA10GR2> exec p
row = X

PL/SQL procedure successfully completed.

b%ORA10GR2> grant execute on p to scott;

Grant succeeded.

b%ORA10GR2> connect scott/tiger
Connected.
scott%ORA10GR2> exec b.p
BEGIN b.p; END;

*
ERROR at line 1:
ORA-00942: table or view does not exist
ORA-02063: preceding line from ORA10GR2@LOOPBACK
ORA-06512: at "B.P", line 4
ORA-06512: at line 1


scott%ORA10GR2> connect b/b
Connected.
b%ORA10GR2> drop database link ora10gr2@loopback;

Database link dropped.

b%ORA10GR2> create database link ora10gr2@loopback connect to b identified by b using 'ora10gr2';

Database link created.

b%ORA10GR2> connect scott/tiger
Connected.
scott%ORA10GR2> exec b.p
row = X

PL/SQL procedure successfully completed.

Many Thanks!!!

February 14, 2008 - 1:59 pm UTC

Reviewer: Carlos from Seattle, USA

Your example was suffice to realize my issue. Thanks, you are an INTERGALACTIC MASTER!!!

Remote databse objects

February 20, 2008 - 4:07 am UTC

Reviewer: Sachin from india

Hi Tom,

Here ,I just want to clear one doubts and i know you can give me suitable answer.

My Question is, if i create synonym based on remote database's objects(Table) and use that synonyms.
and if same thing we do, creating view based same remote database objects and use that in our code.

Just let me know , there are any performance issue with
any of above.

Thanks!!!
Tom Kyte

Followup  

February 20, 2008 - 9:01 am UTC

the main difference between the synonym and the view is that the view will import the metadata into the local instance (user_views will be populated, the column names will be pulled over, their types will be pulled as well)

compilation of that procedure will be easier
you can describe the objects referenced by the procedure (they are in the dictionary)

for this reason alone, I prefer to use views - now the view is dependent on the dblink, not the procedure itself (the procedure could actually compile without doing the over the network processing)

February 22, 2008 - 2:46 am UTC

Reviewer: Sachin from india


means, its just reduse user dependencies...

you are Great!!!






How database links work

February 27, 2008 - 2:21 am UTC

Reviewer: Tengis from UB, Mongolia

Hello Tom, i read Oracle Administrator Guide. There are contents contained "what are database links" or "How to create database link". But i want to know more about dblinks. For example, what happened to open dblink when network failed. Could you please tell me how database links work?
Tom Kyte

Followup  

February 27, 2008 - 2:31 am UTC

they are just network connections - one database is the client of the other.

if the network fails, the link will "fail" when it is detected, eg: you'll get an error.

selecting clob over a dblink

March 12, 2008 - 10:10 am UTC

Reviewer: Michal Pravda from Prague

Hello,

I need to copy data (one way synchronize ideally but not necessary) from table@db1 to table@db2. Dblink exists and works but I can't use it (at least directly) because the table contains two CLOBs. Could you suggest a workaround to ORA-22992 - Cannot use lob locators selected from remote tables?
Tom Kyte

Followup  

March 12, 2008 - 5:35 pm UTC

lobs work over dblinks - are you trying to do things slow by slow perhaps? If you use a nice big bulky single sql statement and erase all of your procedural code, you'll be amazed....

clob copying

March 13, 2008 - 1:40 am UTC

Reviewer: Michal Pravda from Prague

Hi,

I feel like an idiot :(. I haven't actually tried what I asked for.

I was trying to "select" clob over a dblink yesterday which didn't work. After your suggestion a I just tried an "insert select" and that worked. I had a prejudice "no select" then "no insert (select)".

Thank you.

db links

March 29, 2008 - 10:35 am UTC

Reviewer: balakrishna from India.Bangalore


Hi Tom ,

I just want to know if some one has logged into my database using db links , how do i trace this session .can you please help me out.

Regards

Balakrishna
Tom Kyte

Followup  

March 31, 2008 - 8:34 am UTC

if you select program from v$process, for a dedicated connection, you would see

oracle$ORACLE_SID@$hostname

for the remote connection program name (oracle_sid is the sid of the local database, hostname is the hostname of the local database)

There really isn't that much of a difference between a dblink logon and a 'regular' logon, they are both 'regular'

dblink

April 02, 2008 - 12:15 pm UTC

Reviewer: Sam from NJ

Tom, I have question regarding DBLINK.

If I am using a dblibk to query a remote table and using order by or window functions in the query then whose tempory segment ( temp tablespace)it will use . Remote databse where table resides ? or the schema from where I am executing the query ?


Tom Kyte

Followup  

April 02, 2008 - 12:25 pm UTC

either one. it depends on the plan that is generated.

if the sort takes place remotely - it'll use the remote temporary tablespace associated with the user you are connected to the remote instance as.

if the sort takes place locally - it'll use your local temporary tablespace (the one associated with the effective schema executing the query)

DB link

June 11, 2008 - 3:56 pm UTC

Reviewer: Imran from San Antonio, Texas

Hi Tom,

My question is also related to the tpoic DB link,

When I created table usubg database link it got created but I have find that all varcahr2 fields width become increse.

Create table test as select * from test@anotherserver;

Imran
Tom Kyte

Followup  

June 11, 2008 - 8:59 pm UTC

your character sets are different. The remote data is probably single byte and you are probably multi-byte.

It will "grow" the fields so that any string that fit in the other database should fit in yours.

Issues in 10g DBlink???

June 16, 2008 - 12:14 pm UTC

Reviewer: Bhushan from India

Hi Thomas,
Need your suggestions/inputs if you have come across or heard of such a problem.
Let me give you a little background.
We have a application Appl_A which is running on Jrun and connects to a DB (Say APP_DB_8) (8.1.7.4).There are procedures in DB_A which run and populate data in local tables.They connect to a remote DB (8.1.7.4) (say DB_DWH_8) through a DB Link and extract data using select statement.And then a Update is Run on the local table which refers to remote tables as well.Everything is going on fine till now.
I hope you would be clear till here.
Now, Client decided to Migrate and Upgrade the DB to 10g (10.2.0.4).Migrated to a new server and DB upgraded .Now when i try to run a procedure on the new 10g DB, it connects to the same db (DB_DWH_8).The inserts work fine.However when the Update statement is run it takes a very long time.
the scenario is something like this:

Application DB: APP_DB_8
DWH DB: DB_DWH_8
Procedure on APP_DB_8:
Proc1:
--some code--
insert into A (select g,h,j from x@APP_DB_8);
Commit;
--approximately inserts 1.2 Lac Records
Update a set f=b (select w from y@APP_DB_8);
--updates approx. 14k records and then the rest are deleted
commit;
end proc1;
--Proc completes in 10-12 minutes
The same procedure is run on 10g then
insert into A (select g,h,j from x@APP_DB_8); working fine
whereas Update a set f=b (select w from y@APP_DB_8);
runs on and on for hours but never completes. (i waited for 1.5 hours and then killed it)
Is this something related to 10g DB link issue? or do you see there can be any other reason for it?

Thank in Advance,
Bhushan

Tom Kyte

Followup  

June 16, 2008 - 1:49 pm UTC

trace it, compare plans. are they the same?

Trace Plans for above Issue

June 17, 2008 - 5:26 am UTC

Reviewer: Bhushan from India

Hi Thomas,
I could get the trace PLans for the SQL running from 8i to 8i however it takes too long to give the trace plan for the update statement from 10g to 8i.(from sqlplus)
HEre is the trace plan from 8i to 8i from sqlplus
Explain PLan 8i

SQL> UPDATE MYT_COM_PEAM_MASTER PEAM
  2     SET (PEAM_NAME, PEAM_ORG, PEAM_OWNER, PEAM_STATUS) = (SELECT P.PEAM_NAME PEAM_NAME,
  3                                                                  C.PEAM_ORG PEAM_ORG,
  4                                                                  P.PEAM_OWNER,
  5                                                                  C.PEAM_STATUS PEAM_STATUS
  6                                                             FROM PEAM@L_PRDDW       P,
  7                                                                  PEAM_CODES@L_PRDDW C
  8                                                            WHERE UPPER(TRIM(P.PEAM_NAME)) =
  9                                                                  UPPER(TRIM(C.PEAM_NAME))
 10                                                              AND PEAM.SHIPTO_NUMBER =
 11                                                                  P.CUSTNO
 12                                                              AND NVL(UPPER(PEAM.GRADE_CODE),
 13                                                                      'G') =
 14                                                                  NVL(UPPER(P.GRADE_CODE),
 15                                                                      'G')
 16                                                              AND P.COLOR_CODE IS NULL
 17                                                              AND UPPER(C.PEAM_STATUS) =
 18                                                                  'ACTIVE'
 19                                                              AND ROWNUM < 2)
 20   WHERE PEAM_NAME IS NULL
 21     AND PEAM_ORG IS NULL
 22     AND PEAM_STATUS IS NULL;

176199 rows updated.

Elapsed: 00:01:102.97

Execution Plan
----------------------------------------------------------
   0      UPDATE STATEMENT Optimizer=CHOOSE (Cost=40 Card=1 Bytes=43)
   1    0   UPDATE OF 'MYT_COM_PEAM_MASTER'
   2    1     TABLE ACCESS (FULL) OF 'MYT_COM_PEAM_MASTER' (Cost=40 Card=1 Bytes=43)
   3    0   COUNT (STOPKEY)
   4    3     NESTED LOOPS (Cost=3 Card=1 Bytes=77)
   5    4       REMOTE* (Cost=2 Card=1 Bytes=50)                       L_PRDDW.WORLD

   6    4       REMOTE*                                                L_PRDDW.WORLD
   5 SERIAL_FROM_REMOTE            SELECT "PEAM_OWNER","CUSTNO","GRADE_CODE","C
                                   OLOR_CODE","PEAM_NAME" FROM "PEAM" "

   6 SERIAL_FROM_REMOTE            SELECT "PEAM_NAME","PEAM_ORG","PEAM_STATUS"
                                   FROM "PEAM_CODES" "A1" WHERE UPPER(T
Statistics
----------------------------------------------------------
          7  recursive calls
     720705  db block gets
       3909  consistent gets
       1941  physical reads
   85312704  redo size
        516  bytes sent via SQL*Net to client
       2180  bytes received via SQL*Net from client
          4  SQL*Net roundtrips to/from client
          4  sorts (memory)
          0  sorts (disk)
     176199  rows processed

-------------------------------------------
Also,
I could get the explain plan from pl/sql developer for both instances (8i to 8i and 10g to 8i).
Unfortunately i cannot copy paste it here since it does not allow to copy.
One difference i could see is the cost,cardinality and Bytes are exactly the same for fetching the data from remote location.However for update it increases randomly.
When updating using 8i to 8i it is Cost=40,Cardinality=1 and bytes=43 however from 10g to 8i it is cost=234,cardinality=181306 and bytes=3988732.
I hope this helps.

Thanks,
Bhushan

Trace PLan for 10g to 8i

June 17, 2008 - 8:23 am UTC

Reviewer: Bhushan from India

Hi,
I kewp this update running and it gave me this output after 2 to 2.5 hours for 10g to 8i DB LInk(i guess did not look at the winodw after first 30-45 mints)


SQL> UPDATE  MYT_COM_PEAM_MASTER PEAM
  2     SET (PEAM_NAME, PEAM_ORG, PEAM_OWNER, PEAM_STATUS) = (SELECT P.PEAM_NAME PEAM_NAME,
  3                                                                  C.PEAM_ORG PEAM_ORG,
  4                                                                  P.PEAM_OWNER,
  5                                                                  C.PEAM_STATUS PEAM_STATUS
  6                                                             FROM PEAM@L_PRDDW       P,
  7                                                                  PEAM_CODES@L_PRDDW C
  8                                                            WHERE UPPER(TRIM(P.PEAM_NAME)) =
  9                                                                  UPPER(TRIM(C.PEAM_NAME))
 10                                                              AND PEAM.SHIPTO_NUMBER =
 11                                                                  P.CUSTNO
 12                                                              AND NVL(UPPER(PEAM.GRADE_CODE),
 13                                                                      'G') =
 14                                                                  NVL(UPPER(P.GRADE_CODE),
 15                                                                      'G')
 16                                                              AND P.COLOR_CODE IS NULL
 17                                                              AND UPPER(C.PEAM_STATUS) =
 18                                                                  'ACTIVE'
 19                                                              AND ROWNUM < 2)
 20   WHERE PEAM_NAME IS NULL
 21     AND PEAM_ORG IS NULL
 22     AND PEAM_STATUS IS NULL;

176199 rows updated.


Execution Plan
----------------------------------------------------------
   0      UPDATE STATEMENT Optimizer=CHOOSE (Cost=234 Card=181306 Byte
          s=3988732)

   1    0   UPDATE OF 'MYT_COM_PEAM_MASTER'
   2    1     TABLE ACCESS (FULL) OF 'MYT_COM_PEAM_MASTER' (TABLE) (Co
          st=234 Card=181306 Bytes=3988732)

   3    1     COUNT (STOPKEY)
   4    3       NESTED LOOPS (Cost=2 Card=1 Bytes=77)
   5    4         REMOTE* OF 'PEAM_CODES' (REMOTE) (Cost=1 Card=1 Byte L_PRDDW.
          s=27)                                                        WORLD

   6    4         REMOTE* OF 'PEAM' (REMOTE) (Cost=1 Card=1 Bytes=50)  L_PRDDW.
                                                                       WORLD



   5 SERIAL_FROM_REMOTE            SELECT "PEAM_NAME","PEAM_ORG","PEAM_STATUS"
                                   FROM "PEAM_CODES" "A1" WHERE UPPER("

   6 SERIAL_FROM_REMOTE            SELECT "PEAM_OWNER","CUSTNO","GRADE_CODE","C
                                   OLOR_CODE","PEAM_NAME" FROM "PEAM" "



Statistics
----------------------------------------------------------
        269  recursive calls
     712620  db block gets
       1191  consistent gets
        855  physical reads
   87810408  redo size
        454  bytes sent via SQL*Net to client
       1921  bytes received via SQL*Net from client
          3  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
     176199  rows processed

Hope this helps...
If you see the rows processed is the same in the previous posted Explain plan and this..confirming the data is similar..

Regards,
Bhushan Salgar

Tom Kyte

Followup  

June 17, 2008 - 10:01 am UTC

then trace it, see what the waits are and understand - 8i was far out of support before 10g was released, this is an entirely unsupported configuration, anything could be going wrong here and there might be no way to correct or change that.

Any Leads PLease!!!

June 18, 2008 - 1:32 am UTC

Reviewer: Bhushan from India

Yes i agree this is a unsupported configuration for whatever reason, however can we identify loooking at the plan what might be going wrong. Also, i know you will not agree but i changed the following update statement to a for loop and it works OK. Well given a real Life situation where you have no control over the DB version and the infrastructure would you implement the same solution with a Disagreement note at the bottom saying it is working now might not work a year later :)
Here are the statements...

UPdate Statement:
UPDATE MYT_COM_PEAM_MASTER peam
SET (peam_name
,peam_org
,peam_owner
,peam_status
)
=
(SELECT
p.peam_name peam_name
,c.peam_org peam_org
,p.peam_owner
,c.peam_status peam_status
FROM
peam@l_prddw p
,peam_codes@l_prddw c
WHERE
UPPER(trim(p.peam_name))=UPPER(trim(c.peam_name))
AND
peam.shipto_number = p.custno
AND
NVL(UPPER(peam.grade_code),'G') = NVL(UPPER(p.grade_code),'G')
AND
p.color_code IS NULL
AND
UPPER(c.peam_status) = 'ACTIVE'

AND
ROWNUM < 2
)
WHERE
peam_name IS NULL
AND
peam_org IS NULL
AND
peam_status IS NULL;

Changed to a For Loop (Kindly note the loop iteration is only ONCE)

FOR x IN (SELECT
p.peam_name peam_name
,c.peam_org peam_org
,p.peam_owner
,c.peam_status peam_status
FROM
peam@l_prddw p
,peam_codes@l_prddw c,
MYT_COM_PEAM_MASTER peam
WHERE
UPPER(trim(p.peam_name))=UPPER(trim(c.peam_name))
AND
peam.shipto_number = p.custno
AND
NVL(UPPER(peam.grade_code),'G') = NVL(UPPER(p.grade_code),'G')
AND
p.color_code IS NULL
AND
UPPER(c.peam_status) = 'ACTIVE'

AND
ROWNUM < 2) LOOP
UPDATE MYT_COM_PEAM_MASTER SET peam_name=x.peam_name,
peam_org=x.peam_org,
peam_owner=x.peam_owner,
peam_status=x.peam_status WHERE peam_name IS NULL
AND
peam_org IS NULL
AND
peam_status IS NULL;
commit;
END LOOP;


Tom Kyte

Followup  

June 18, 2008 - 1:07 pm UTC

I thought you said the plans were the same. They look the same - so it wasn't due to a plan change. What I just said above stands:


then trace it, see what the waits are
and understand - 8i was far out of support before 10g was released, this is an entirely unsupported configuration, anything could be going wrong here and there might be no way to correct or change that.

different plan while using dblink

July 21, 2008 - 9:47 pm UTC

Reviewer: A reader

Hi Tom,

I have two schema, F_ORDER_LINE & L_AD_SLOT_PROPORTION table is under RAPT_BDDM schema, while T_ORDER_LINE_TOTAL_PROPORTION is in schema RAPT_UDM.
When I ran my query it took more then 1 hr for processing 4 months data, so I was trying different way to tune the query (as per my little knowledge) I am running this query from RAPT_UDM user and accessing RAPT_BDDM tables. Earlier I was accessing both the tables via SCHEMA_NAME.TABLE_TABLE method, then I have created synonym in rapt_udm which is poining to rapt_bddm table (synonym created schema_name.table_name method only) and both the way it is taking more then 1 hr. Then I created db link in RAPT_UDM schema and then created synonyum via table_name@db_link and surpricely it is taking 23 minuts.
Below is the explain plan for all differn way when i access tables via schema_name.table name or synonym (which is created schema_name.table_name) it is showing 1hr 44 minutes while dblink method showind 27 second, can u explain why it is showing that much changes in the plan. i am the only user connected to the database and there is no other activity is going on. I have tryied no. of times but i got the same diff.

18:07:42 DNUD>@dnbd
Connected.
18:07:48 NBD>show user
USER is "RAPT_BDDM"
18:07:50 NBD>desc f_order_line
Name
---------------------------------------------------------
ORDER_ID
ORDER_LINE_ID
SCHEDULED_DATE
ORDER_NAME
ORDER_DATE
PLACEMENT_ID
AD_COMPONENT_ID
INVENTORY_TYPE_ID
CUSTOMER_ID
AGENCY_ID
SCHEDULED_IMPRESSIONS
EXTENDED_SALES_PRICE
EXTENDED_LIST_PRICE
EXTENDED_FLOOR_PRICE
REMNANT_REVENUE_CPM
ADJUSTMENT_IMPRESSIONS
ADJUSTMENT_SALES_PRICE
FLIGHT_START_DATE
FLIGHT_END_DATE
DAY_OF_WEEK
PRICING_TYPE_ID
PACKAGE_ID
ORDER_TYPE_ID
CLUSTER_TYPE_ID
DELIVERY_TYPE_ID

18:07:59 NBD>grant all on f_order_line to rapt_udm;

Grant succeeded.

18:08:19 NBD>@dnudm
Connected.
18:08:27 DNUD>desc rapt_bddm.f_order_line
Name
---------------------------------------------------------
ORDER_ID
ORDER_LINE_ID
SCHEDULED_DATE
ORDER_NAME
ORDER_DATE
PLACEMENT_ID
AD_COMPONENT_ID
INVENTORY_TYPE_ID
CUSTOMER_ID
AGENCY_ID
SCHEDULED_IMPRESSIONS
EXTENDED_SALES_PRICE
EXTENDED_LIST_PRICE
EXTENDED_FLOOR_PRICE
REMNANT_REVENUE_CPM
ADJUSTMENT_IMPRESSIONS
ADJUSTMENT_SALES_PRICE
FLIGHT_START_DATE
FLIGHT_END_DATE
DAY_OF_WEEK
PRICING_TYPE_ID
PACKAGE_ID
ORDER_TYPE_ID
CLUSTER_TYPE_ID
DELIVERY_TYPE_ID
NUMBER

18:08:36 DNUD>show user
USER is "RAPT_UDM"
18:09:25 DNUD>create synonym bddm_f_order_line for rapt_bddm.f_order_line;

Synonym created.

Elapsed: 00:00:00.46
18:09:44 DNUD>desc bddm_f_order_line
Name Null? Type
Name
---------------------------------------------------------
ORDER_ID
ORDER_LINE_ID
SCHEDULED_DATE
ORDER_NAME
ORDER_DATE
PLACEMENT_ID
AD_COMPONENT_ID
INVENTORY_TYPE_ID
CUSTOMER_ID
AGENCY_ID
SCHEDULED_IMPRESSIONS
EXTENDED_SALES_PRICE
EXTENDED_LIST_PRICE
EXTENDED_FLOOR_PRICE
REMNANT_REVENUE_CPM
ADJUSTMENT_IMPRESSIONS
ADJUSTMENT_SALES_PRICE
FLIGHT_START_DATE
FLIGHT_END_DATE
DAY_OF_WEEK
PRICING_TYPE_ID
PACKAGE_ID
ORDER_TYPE_ID
CLUSTER_TYPE_ID
DELIVERY_TYPE_ID
NUMBER

18:09:49 DNUD>
18:09:50 DNUD>set autot traceonly explain
18:10:07 DNUD>SELECT
18:10:23 2 sfolt.order_id
18:10:23 3 ,sfolt.order_line_id
18:10:23 4 ,scheduled_date
18:10:23 5 ,ad_slot_id
18:10:23 6 ,ad_component_id
18:10:23 7 ,inventory_type_id
18:10:23 8 ,delivery_type_id
18:10:23 9 ,(case when nvl(scheduled_impressions,0) <> 0 then (extended_sales_price/scheduled_impressions)*1000 else null end) cpm
18:10:23 10 ,scheduled_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) scheduled_impressions
18:10:23 11 ,extended_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_sales_price
18:10:23 12 ,extended_list_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_list_price
18:10:23 13 ,extended_floor_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_floor_price
18:10:23 14 ,remnant_revenue_cpm * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) remnant_revenue_cpm
18:10:23 15 ,adjustment_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_impressions
18:10:23 16 ,adjustment_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_sales_price
18:10:23 17 ,sum(sfolt.scheduled_impressions/(sfolt.flight_end_date - sfolt.flight_start_date +1)) over ( partition by sfolt.order_id, sfolt.order_line_id order by sfolt.order_id, sfolt.order_line_id) total_impressions
18:10:24 18 FROM
18:10:24 19 T_ORDER_LINE_TOTAL_PROPORTION tp
18:10:24 20 ,bddm_f_order_line sfolt
18:10:24 21 ,rapt_bddm.l_ad_slot_proportion lptp
18:10:24 22 WHERE
18:10:24 23 tp.order_id = sfolt.order_id
18:10:24 24 AND tp.order_line_id = sfolt.order_line_id
18:10:24 25 AND tp.flight_start_date = sfolt.flight_start_date
18:10:24 26 AND tp.flight_end_date = sfolt.flight_end_date
18:10:24 27 AND sfolt.placement_id = lptp.placement_id
18:10:24 28 AND sfolt.day_of_week = lptp.day_of_week
18:10:24 29 and scheduled_date between '01-apr-2008' and '31-jul-2008'
18:10:24 30 and proportion_month = '01-JUN-2008'
18:10:24 31 /
Elapsed: 00:00:00.34

Execution Plan
----------------------------------------------------------
Plan hash value: 1447296416

----------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Pstart| Pstop |
----------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 9381K| 2192M| | 523K (1)| 01:44:42 | | |
| 1 | WINDOW SORT | | 9381K| 2192M| 4728M| 523K (1)| 01:44:42 | | |
|* 2 | HASH JOIN | | 9381K| 2192M| | 25071 (4)| 00:05:01 | | |
|* 3 | HASH JOIN | | 8634 | 1652K| 3992K| 8077 (2)| 00:01:37 | | |
| 4 | TABLE ACCESS FULL | T_ORDER_LINE_TOTAL_PROPORTION | 60920 | 3272K| | 119 (3)| 00:00:02 | | |
|* 5 | TABLE ACCESS FULL | F_ORDER_LINE | 165K| 22M| | 6557 (2)| 00:01:19 | | |
| 6 | PARTITION RANGE SINGLE| | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 |
|* 7 | TABLE ACCESS FULL | L_AD_SLOT_PROPORTION | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 |
----------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("SFOLT"."PLACEMENT_ID"="LPTP"."PLACEMENT_ID" AND "SFOLT"."DAY_OF_WEEK"="LPTP"."DAY_OF_WEEK")
3 - access("TP"."ORDER_ID"="SFOLT"."ORDER_ID" AND "TP"."ORDER_LINE_ID"="SFOLT"."ORDER_LINE_ID" AND
"TP"."FLIGHT_START_DATE"="SFOLT"."FLIGHT_START_DATE" AND "TP"."FLIGHT_END_DATE"="SFOLT"."FLIGHT_END_DATE")
5 - filter("SCHEDULED_DATE">=TO_DATE('2008-04-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND
"SCHEDULED_DATE"<=TO_DATE('2008-07-31 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
7 - filter("PROPORTION_MONTH"=TO_DATE('2008-06-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))


18:10:41 DNUD>ed
Wrote file afiedt.buf

1 SELECT
2 sfolt.order_id
3 ,sfolt.order_line_id
4 ,scheduled_date
5 ,ad_slot_id
6 ,ad_component_id
7 ,inventory_type_id
8 ,delivery_type_id
9 ,(case when nvl(scheduled_impressions,0) <> 0 then (extended_sales_price/scheduled_impressions)*1000 else null end) cpm
10 ,scheduled_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) scheduled_impressions
11 ,extended_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_sales_price
12 ,extended_list_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_list_price
13 ,extended_floor_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_floor_price
14 ,remnant_revenue_cpm * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) remnant_revenue_cpm
15 ,adjustment_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_impressions
16 ,adjustment_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_sales_price
17 ,sum(sfolt.scheduled_impressions/(sfolt.flight_end_date - sfolt.flight_start_date +1)) over ( partition by sfolt.order_id, sfolt.order_line_id order by sfolt.order_id, sfolt.order_line_id) total_impressions
18 FROM
19 T_ORDER_LINE_TOTAL_PROPORTION tp
20 ,rapt_bddm.f_order_line sfolt
21 ,rapt_bddm.l_ad_slot_proportion lptp
22 WHERE
23 tp.order_id = sfolt.order_id
24 AND tp.order_line_id = sfolt.order_line_id
25 AND tp.flight_start_date = sfolt.flight_start_date
26 AND tp.flight_end_date = sfolt.flight_end_date
27 AND sfolt.placement_id = lptp.placement_id
28 AND sfolt.day_of_week = lptp.day_of_week
29 and scheduled_date between '01-apr-2008' and '31-jul-2008'
30* and proportion_month = '01-JUN-2008'
18:10:52 DNUD>/
Elapsed: 00:00:00.34

Execution Plan
----------------------------------------------------------
Plan hash value: 1447296416

----------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Pstart| Pstop |
----------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 9381K| 2192M| | 523K (1)| 01:44:42 | | |
| 1 | WINDOW SORT | | 9381K| 2192M| 4728M| 523K (1)| 01:44:42 | | |
|* 2 | HASH JOIN | | 9381K| 2192M| | 25071 (4)| 00:05:01 | | |
|* 3 | HASH JOIN | | 8634 | 1652K| 3992K| 8077 (2)| 00:01:37 | | |
| 4 | TABLE ACCESS FULL | T_ORDER_LINE_TOTAL_PROPORTION | 60920 | 3272K| | 119 (3)| 00:00:02 | | |
|* 5 | TABLE ACCESS FULL | F_ORDER_LINE | 165K| 22M| | 6557 (2)| 00:01:19 | | |
| 6 | PARTITION RANGE SINGLE| | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 |
|* 7 | TABLE ACCESS FULL | L_AD_SLOT_PROPORTION | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 |
----------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("SFOLT"."PLACEMENT_ID"="LPTP"."PLACEMENT_ID" AND "SFOLT"."DAY_OF_WEEK"="LPTP"."DAY_OF_WEEK")
3 - access("TP"."ORDER_ID"="SFOLT"."ORDER_ID" AND "TP"."ORDER_LINE_ID"="SFOLT"."ORDER_LINE_ID" AND
"TP"."FLIGHT_START_DATE"="SFOLT"."FLIGHT_START_DATE" AND "TP"."FLIGHT_END_DATE"="SFOLT"."FLIGHT_END_DATE")
5 - filter("SCHEDULED_DATE">=TO_DATE('2008-04-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss') AND
"SCHEDULED_DATE"<=TO_DATE('2008-07-31 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))
7 - filter("PROPORTION_MONTH"=TO_DATE('2008-06-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))

18:10:53 DNUD>
18:10:56 DNUD>
18:10:57 DNUD>
18:10:57 DNUD>DROP SYNONYM BDDM_F_ORDER_LINE;

Synonym dropped.

Elapsed: 00:00:00.62
18:13:25 DNUD>CREATE SYNONYM BDDM_F_ORDER_LINE FOR F_ORDER_LINE@BDLINK;

Synonym created.

18:13:58 DNUD>ED

18:14:08 DNUD>
18:14:21 DNUD>SELECT
18:14:22 2 sfolt.order_id
18:14:22 3 ,sfolt.order_line_id
18:14:22 4 ,scheduled_date
18:14:22 5 ,ad_slot_id
18:14:22 6 ,ad_component_id
18:14:22 7 ,inventory_type_id
18:14:22 8 ,delivery_type_id
18:14:22 9 ,(case when nvl(scheduled_impressions,0) <> 0 then (extended_sales_price/scheduled_impressions)*1000 else null end) cpm
18:14:22 10 ,scheduled_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) scheduled_impressions
18:14:22 11 ,extended_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_sales_price
18:14:22 12 ,extended_list_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_list_price
18:14:22 13 ,extended_floor_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_floor_price
18:14:22 14 ,remnant_revenue_cpm * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) remnant_revenue_cpm
18:14:22 15 ,adjustment_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_impressions
18:14:22 16 ,adjustment_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_sales_price
18:14:22 17 ,sum(sfolt.scheduled_impressions/(sfolt.flight_end_date - sfolt.flight_start_date +1)) over ( partition by sfolt.order_id, sfolt.order_line_id order by sfolt.order_id, sfolt.order_line_id) total_impressions
18:14:23 18 FROM
18:14:23 19 T_ORDER_LINE_TOTAL_PROPORTION tp
18:14:23 20 ,bddm_f_order_line sfolt
18:14:23 21 ,rapt_bddm.l_ad_slot_proportion lptp
18:14:23 22 WHERE
18:14:23 23 tp.order_id = sfolt.order_id
18:14:23 24 AND tp.order_line_id = sfolt.order_line_id
18:14:23 25 AND tp.flight_start_date = sfolt.flight_start_date
18:14:23 26 AND tp.flight_end_date = sfolt.flight_end_date
18:14:23 27 AND sfolt.placement_id = lptp.placement_id
18:14:23 28 AND sfolt.day_of_week = lptp.day_of_week
18:14:23 29 and scheduled_date between '01-apr-2008' and '31-jul-2008'
18:14:23 30 and proportion_month = '01-JUN-2008'
18:14:23 31 /
Elapsed: 00:00:00.36

Execution Plan
----------------------------------------------------------
Plan hash value: 3101442654

--------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Pstart| Pstop | Inst |IN-OUT|
--------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1724K| 494M| | 135K (1)| 00:27:12 | | | | |
| 1 | WINDOW SORT | | 1724K| 494M| 1077M| 135K (1)| 00:27:12 | | | | |
|* 2 | HASH JOIN | | 1724K| 494M| | 24158 (4)| 00:04:50 | | | | |
|* 3 | HASH JOIN | | 1587 | 390K| 3992K| 7165 (2)| 00:01:26 | | | | |
| 4 | TABLE ACCESS FULL | T_ORDER_LINE_TOTAL_PROPORTION | 60920 | 3272K| | 119 (3)| 00:00:02 | | | | |
| 5 | REMOTE | F_ORDER_LINE | 30482 | 5864K| | 6548 (2)| 00:01:19 | | | BDLINK | R->S |
| 6 | PARTITION RANGE SINGLE| | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 | | |
|* 7 | TABLE ACCESS FULL | L_AD_SLOT_PROPORTION | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 | | |
--------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("SFOLT"."PLACEMENT_ID"="LPTP"."PLACEMENT_ID" AND "SFOLT"."DAY_OF_WEEK"="LPTP"."DAY_OF_WEEK")
3 - access("TP"."ORDER_ID"="SFOLT"."ORDER_ID" AND "TP"."ORDER_LINE_ID"="SFOLT"."ORDER_LINE_ID" AND
"TP"."FLIGHT_START_DATE"="SFOLT"."FLIGHT_START_DATE" AND "TP"."FLIGHT_END_DATE"="SFOLT"."FLIGHT_END_DATE")
7 - filter("PROPORTION_MONTH"=TO_DATE('2008-06-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))

Remote SQL Information (identified by operation id):
----------------------------------------------------

5 - SELECT "ORDER_ID","ORDER_LINE_ID","SCHEDULED_DATE","PLACEMENT_ID","AD_COMPONENT_ID","INVENTORY_TYPE_ID","SCHEDULED_IMPRESSIONS","EX
TENDED_SALES_PRICE","EXTENDED_LIST_PRICE","EXTENDED_FLOOR_PRICE","REMNANT_REVENUE_CPM","ADJUSTMENT_IMPRESSIONS","ADJUSTMENT_SALES_PRICE","
FLIGHT_START_DATE","FLIGHT_END_DATE","DAY_OF_WEEK","DELIVERY_TYPE_ID" FROM "F_ORDER_LINE" "SFOLT" WHERE "SCHEDULED_DATE"<=:1 AND
"SCHEDULED_DATE">=:2 (accessing 'BDLINK' )



different plan by using dblink (better)

July 21, 2008 - 9:49 pm UTC

Reviewer: A reader

18:10:57 DNUD>DROP SYNONYM BDDM_F_ORDER_LINE;

Synonym dropped.

Elapsed: 00:00:00.62
18:13:25 DNUD>CREATE SYNONYM BDDM_F_ORDER_LINE FOR F_ORDER_LINE@BDLINK;

Synonym created.

18:13:58 DNUD>ED

18:14:08 DNUD>
18:14:21 DNUD>SELECT
18:14:22 2 sfolt.order_id
18:14:22 3 ,sfolt.order_line_id
18:14:22 4 ,scheduled_date
18:14:22 5 ,ad_slot_id
18:14:22 6 ,ad_component_id
18:14:22 7 ,inventory_type_id
18:14:22 8 ,delivery_type_id
18:14:22 9 ,(case when nvl(scheduled_impressions,0) <> 0 then (extended_sales_price/scheduled_impressions)*1000 else null end) cpm
18:14:22 10 ,scheduled_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) scheduled_impressions
18:14:22 11 ,extended_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_sales_price
18:14:22 12 ,extended_list_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_list_price
18:14:22 13 ,extended_floor_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) extended_floor_price
18:14:22 14 ,remnant_revenue_cpm * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) remnant_revenue_cpm
18:14:22 15 ,adjustment_impressions * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_impressions
18:14:22 16 ,adjustment_sales_price * (CASE WHEN total_proportion = 0 THEN 1/total_ad_slot ELSE proportion/total_proportion END) adjustment_sales_price
18:14:22 17 ,sum(sfolt.scheduled_impressions/(sfolt.flight_end_date - sfolt.flight_start_date +1)) over ( partition by sfolt.order_id, sfolt.order_line_id order by sfolt.order_id, sfolt.order_line_id) total_impressions
18:14:23 18 FROM
18:14:23 19 T_ORDER_LINE_TOTAL_PROPORTION tp
18:14:23 20 ,bddm_f_order_line sfolt
18:14:23 21 ,rapt_bddm.l_ad_slot_proportion lptp
18:14:23 22 WHERE
18:14:23 23 tp.order_id = sfolt.order_id
18:14:23 24 AND tp.order_line_id = sfolt.order_line_id
18:14:23 25 AND tp.flight_start_date = sfolt.flight_start_date
18:14:23 26 AND tp.flight_end_date = sfolt.flight_end_date
18:14:23 27 AND sfolt.placement_id = lptp.placement_id
18:14:23 28 AND sfolt.day_of_week = lptp.day_of_week
18:14:23 29 and scheduled_date between '01-apr-2008' and '31-jul-2008'
18:14:23 30 and proportion_month = '01-JUN-2008'
18:14:23 31 /
Elapsed: 00:00:00.36

Execution Plan
----------------------------------------------------------
Plan hash value: 3101442654

--------------------------------------------------------------------------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |TempSpc| Cost (%CPU)| Time | Pstart| Pstop | Inst |IN-OUT|
--------------------------------------------------------------------------------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1724K| 494M| | 135K (1)| 00:27:12 | | | | |
| 1 | WINDOW SORT | | 1724K| 494M| 1077M| 135K (1)| 00:27:12 | | | | |
|* 2 | HASH JOIN | | 1724K| 494M| | 24158 (4)| 00:04:50 | | | | |
|* 3 | HASH JOIN | | 1587 | 390K| 3992K| 7165 (2)| 00:01:26 | | | | |
| 4 | TABLE ACCESS FULL | T_ORDER_LINE_TOTAL_PROPORTION | 60920 | 3272K| | 119 (3)| 00:00:02 | | | | |
| 5 | REMOTE | F_ORDER_LINE | 30482 | 5864K| | 6548 (2)| 00:01:19 | | | BDLINK | R->S |
| 6 | PARTITION RANGE SINGLE| | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 | | |
|* 7 | TABLE ACCESS FULL | L_AD_SLOT_PROPORTION | 11M| 523M| | 16829 (4)| 00:03:22 | 2 | 2 | | |
--------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("SFOLT"."PLACEMENT_ID"="LPTP"."PLACEMENT_ID" AND "SFOLT"."DAY_OF_WEEK"="LPTP"."DAY_OF_WEEK")
3 - access("TP"."ORDER_ID"="SFOLT"."ORDER_ID" AND "TP"."ORDER_LINE_ID"="SFOLT"."ORDER_LINE_ID" AND
"TP"."FLIGHT_START_DATE"="SFOLT"."FLIGHT_START_DATE" AND "TP"."FLIGHT_END_DATE"="SFOLT"."FLIGHT_END_DATE")
7 - filter("PROPORTION_MONTH"=TO_DATE('2008-06-01 00:00:00', 'yyyy-mm-dd hh24:mi:ss'))

Remote SQL Information (identified by operation id):
----------------------------------------------------

5 - SELECT "ORDER_ID","ORDER_LINE_ID","SCHEDULED_DATE","PLACEMENT_ID","AD_COMPONENT_ID","INVENTORY_TYPE_ID","SCHEDULED_IMPRESSIONS","EX
TENDED_SALES_PRICE","EXTENDED_LIST_PRICE","EXTENDED_FLOOR_PRICE","REMNANT_REVENUE_CPM","ADJUSTMENT_IMPRESSIONS","ADJUSTMENT_SALES_PRICE","
FLIGHT_START_DATE","FLIGHT_END_DATE","DAY_OF_WEEK","DELIVERY_TYPE_ID" FROM "F_ORDER_LINE" "SFOLT" WHERE "SCHEDULED_DATE"<=:1 AND
"SCHEDULED_DATE">=:2 (accessing 'BDLINK' )



Different Versions of oracle

July 23, 2008 - 3:37 pm UTC

Reviewer: Scott from New York, NY, USA

Tom,
Are DB Links compatible with different versions of Oracle? My 10g database can use the link to access my 9i, but I am having issues with my 9i accessing my 10g. Is this a software limitation?

Thanks,
Scott
Tom Kyte

Followup  

July 24, 2008 - 10:44 am UTC

it should work - all supported releases should work - please utilize support.

database links from 10g to 9i

July 29, 2008 - 7:24 pm UTC

Reviewer: kevin from san francisco, ca

I seem to be experiencing the same issue. I can create a db link and successfully query from 10g (10.2.0.4) to 9i (9.2.0.8) but not from 9i to 10g. The tnsnames entry appears fine on the 9i side, I can successfully connect to 9i from the 10g host using sqlplus and tnsnames alias. BUT, when I:
create database link mylink
connect to <user> identified by <pword>
using 'samealiasiusedforsqlplusconnect';

and issue select sysdate from dual@mylink; I get an error about name resolution. Yes, I will follow-up with support but just wanted to provide a real example of the problem the other reader was apparently experiencing. Thanks.
Tom Kyte

Followup  

August 01, 2008 - 11:03 am UTC

no error, no able to comment very much

but if it is saying "unable to resolve your tnsnames" stuff, that has nothing to do with versions - everything to do with the configuration on the 9i side, you are reading the wrong tnsnames.ora file or the right one does not have this tns connect entry set in it.

to "prove" that

create database link .... using '(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=...(SERVICE_NAME=ora10gr2)))'


just put the tns entry right in there.

db links

July 29, 2008 - 9:16 pm UTC

Reviewer: kevin from san francisco, usa

...update to previous. Adding the env variable TNS_ADMIN to where the listener is run from and tnsnames.ora entries are held solved the problem.
Tom Kyte

Followup  

August 02, 2008 - 4:56 pm UTC

you were reading the wrong tnsnames.ora file then... tns_admin tells us where to find it instead of looking in the default paths first.

August 05, 2008 - 2:06 pm UTC

Reviewer: Alexander

Tom,

Can I have you opionion on the following. If I am using a 10.2.0.2 database to connect to a 10.2.0.4 database via db link, should I expect this:

SQL> merge into ebr.vin_mask a
  2  using
  3  (
  4  select * from ebr.vin_mask@orac01x
  5   minus
  6  select * from ebr.vin_mask
  7  ) b
  8  on (a.vin_make_code = b.vin_make_code
  9  and a.mask_position = b.mask_position
 10  and a.model_year = b.model_year
 11  and 1 = 0)
 12  -- when matched then / This can't happen these columns are pks /
 13  -- update
 14  --   set a.vin_make_code = b.vin_make_code,
 15  --       a.mask_position = b.mask_position,
 16  --       a.model_year = b.model_year
 17  when not matched then
 18  insert(
 19     a.vin_make_code,
 20     a.mask_position,
 21     a.model_year
 22  ) values(
 23     b.vin_make_code,
 24     b.mask_position,
   b.model_year
 25   26  );
merge into ebr.vin_mask a
               *
ERROR at line 1:
ORA-02064: distributed operation not supported


When I go test ===> dev, (both 10.2.0.4), this does not happen. There are no unsupported columns.

SQL> desc ebr.vin_mask
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 VIN_MAKE_CODE                             NOT NULL CHAR(10)
 MASK_POSITION                             NOT NULL CHAR(1)
 MODEL_YEAR                                NOT NULL NUMBER(4)


This only strange thing is, when I hit the issue, it's within a job with half a dozen other merge's very similar to the one that is failing, but they all work.

Also, global_names is set to true on the 10.2.0.4 instances, not in the problematic 10.2.0.2.

I did however try it using alter session, it still bombed. Do you have any ideas? Really appreciate it.
Tom Kyte

Followup  

August 05, 2008 - 6:34 pm UTC

contact support, reference bug #4311273

Dblink and network problems

August 20, 2008 - 7:05 am UTC

Reviewer: setadini from Italy

I'm running a web-site backend database with oracle XE and many other remote db's (all of them are 10gR2 Standard or Enterprise) are syncronizing their schemas on this machine via dblink via bi-directional insert/select statements.

The syncronize procedure is run every 5 minutes on the "remote" databases without any problem.

When a network error happens during a syncronization, sometimes the remote session remains busy with the event "SQL*Net message from dblink" (for days...) and even killing it no other session is able to use the (network-restored) dblink until a shutdown.
Is there a way or special syntax to make the session expire/timeout to avoid the shutdown?

Thanks

Atlast i know the reason!!!

August 21, 2008 - 7:46 am UTC

Reviewer: Bhushan from India

Hi Thomas,
You know what is the best way to keep one busy and gain knowledge without being bored..Read asktom.oracle .com ;)
Anyways..i had asked a question sometime back about the issues in 10g DBlink to 8i DB's and you answered there might be a way to correct it or might not..the 8i configuration is not supported any more.
Well i did find out there is a way :)
well it was all about
alter session set optimizer_index_cost_adj=35
and i do not have to use the RBO the CBO works even better then the RBO now.

Well good thing: I found it on your own site
Bad thing: Will have to convince the client again ;)

Cheers,
Bhushan
Tom Kyte

Followup  

August 21, 2008 - 8:39 am UTC

umm, sorry to disappoint, but that optimizer setting will have no impact on your ability to connect or not connect 10g to 8i. It may or may not work depending on what you do (never tested internally), but that optimizer setting has *nothing* to do with the ability to connect or not.

export/import public db links using exp/imp

September 10, 2008 - 1:32 am UTC

Reviewer: A reader

How can I export/import public dblinks using exp/imp

I am exporting importing 2 schemas from a Database and these Schemas also use public DB links in the source schema.I dont want to do a full exp/imp as I am only interested in 2 schemas.
How to export/import public dblinks.
One way could be to recreate them manually, But is there any exp imp option for this ?
something like
exp userid/pass owner=schema_1,schema_2,PUBLIC

IMP userid/pass FROMUSER=schema_1,schema_2,PUBLIC TOUSER=schema_1,schema_2,PUBLIC.

Thanx
Tom Kyte

Followup  

September 11, 2008 - 10:37 am UTC

you cannot, you'll have to recreate them. when you export at the schema level, only things owned by the schema come - the public database links are not owned by the schema.

db 9208 export/import public db links using exp/imp

September 10, 2008 - 1:34 am UTC

Reviewer: A reader

Sorry forgot Db version is 9208
export/import public db links using exp/imp

Compiled code and datbase links

September 10, 2008 - 11:01 am UTC

Reviewer: Mike from Cleveland, OH USA

I have a setup like this:

Oracle1 has user SchemaA which owns table T.
Oracle2 has user SchemaA which owns:
- Synonym T which points to SchemaA.T@Oracle1. (DB link Oracle1 is a public link to Oracle1 with no CONNECT TO clause or other authentication. Passwords match for SchemaA on Oracle1 and Oracle2.)
- Package P. Package P has SELECT and INSERT calls to a table-like object called T, which is supposed to resolve using the synonym above.


On Oracle2, we have issued GRANT EXECUTE ON SchemaA.P TO ExecutionUserB.

In SQLPlus, we connect as ExecutionUserB@Oracle2 and run an anonymous block to execute SchemaA.P.

Now, the problem. It seems that the credentials being used over the link are those of ExecutionUserB, not SchemaA. I thought that, since the link is being used by compiled code, the SELECT, INSERT, etc. calls would have the credentials of the owner of the code.

Is this the expected behavior? Or is there some piece of the puzzle I am missing? I can 'fix' this by creating a link with the credentials I want, but that makes for one more headache when passwords change.
Tom Kyte

Followup  

September 11, 2008 - 11:07 am UTC

... Now, the problem. It seems that the credentials being used over the link are
those of ExecutionUserB, not SchemaA. I thought that, since the link is being
used by compiled code, the SELECT, INSERT, etc. calls would have the
credentials of the owner of the code.
....

not for current user database links - the password needs to be sent from database 1 to database 2 - we do not have the password stored for the owner of the procedure, we only have the current users credentials.

You would have to create the link with the desired set of credentials if you wanted them to be "constant"

About ORA-02064

September 11, 2008 - 9:23 am UTC

Reviewer: Vijay Bhaskar from India

Tom,

Could you please elaborate your comment..

"you cannot do transactional control over a dblink - the remote site isn't allowed to commit......"

If so then, are't we violating the above, when RPC calls (not involving OUT variables) runs fine ?

Further, the workaround you suggested as above, may not fit for all. For example, in our case :-
We have
dbase A :-
--------
proc a(accepts OUT params & containts "commits")
This proc also has an "insert" statement which logs an entry(invoker's details)into a local tables whenever it's being invoked.

A user(say SCOTT) in dbase B invokes the above procedure "a", through RPC call...

in dbase B :- exec a@A.world;

now it would fail with ORA-02064. To avoid this I have to remote commit..& thereby, rely on invoker to commit, so that i can see the log record in dbase A. If he decides to rollback otherwise, i will loose the information. isn't ?

So, this in a way, introduces dependency on B...

Can you please throw some light on this.

Regards,

Vijay


Tom Kyte

Followup  

September 16, 2008 - 12:21 pm UTC

... If so then, are't we violating the above, when RPC calls (not involving OUT
variables) runs fine ?
...

explain why you think so? I don't think so...

... Further, the workaround you suggested as above, may not fit for all. For
example ...

explain again, this is a HUGE page, "as above" could mean hundreds of things in this context.



Proc A is not allowed to have a commit, the invoker - from database B would do the commit.



There is no dependency here - the site that initiated the dblink OWNS the transaction. Database B in your case is the site that would commit. Proc A should NOT have a commit, it would be executed from database B and B would commit.

What I'm trying to say is...

September 30, 2008 - 8:48 am UTC

Reviewer: Vijay Bhaskar from India

Tom,

Thanks a ton for your response. I might not have able to properly understand your point.

Let me explain the point I'm trying to make

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 - 64bi
PL/SQL Release 10.1.0.3.0 - Production
CORE    10.1.0.3.0      Production
TNS for HPUX: Version 10.1.0.3.0 - Production
NLSRTL Version 10.1.0.3.0 - Production
SQL>
SQL> select * from global_name;

GLOBAL_NAME
--------------------------------------
BIP2D2.DEVENV1.BT.CO.UK

SQL> 
SQL> sho user
USER is "SCOTT"
SQL>
SQL> create table t_user_data(
  2    userid varchar2(10)
  3    ,username varchar2(30)
  4    ,hiredate date
  5    ,last_logged_in timestamp(6)
  6  )
  7  tablespace appl_data
  8  /

Table created.
SQL> alter table t_user_data add constraint t_user_data_pk primary key(userid);

Table altered.
SQL> 
SQL> insert into t_user_data values('E1','Vijay',to_date('09/08/2008','dd/mm/yyyy'),null);

1 row created.

SQL> commit;

Commit complete.
SQL> set lin 990
SQL> 
SQL> select * from t_user_data;

USERID     USERNAME                       HIREDATE  LAST_LOGGED_IN
---------- ------------------------------ --------- ---------------------
E1         Vijay                          09-AUG-08

SQL> 
SQL> create or replace procedure pr_last_login(uid t_user_data.userid%type)
  2  as
  3  begin
  4    update t_user_data set last_logged_in=systimestamp where userid=uid;
  5    if sql%notfound then
  6      raise_application_error(-20001,'User '||uid||' is not registered !');
  7    end if;
  8    commit;
  9  end;
 10  /

Procedure created.
SQL> 


Then I logged onto another database (invoking) named BIP2T2 as SCOTT :-


SQL*Plus: Release 10.2.0.1.0 - Production on Tue Sep 30 17:13:28 2008

Copyright (c) 1982, 2005, Oracle.  All rights reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security, OLAP and Data Mining Scoring Engine options

SQL> 
SQL> 
SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.1.0.3.0 - 64bi
PL/SQL Release 10.1.0.3.0 - Production
CORE    10.1.0.3.0      Production
TNS for HPUX: Version 10.1.0.3.0 - Production
NLSRTL Version 10.1.0.3.0 - Production

SQL> 
SQL> 
SQL> select * from global_name;

GLOBAL_NAME
--------------------------------------------------------------------------------
BIP2T2.DEVENV1.BT.CO.UK

SQL> sho user
USER is "SCOTT"
SQL> 

Created a database link called BIP2D2.DEVENV1.BT.CO.UK pointing, as the name implies, to BIP2D2 database.
SQL>
SQL> create database link bip2d2.devenv1.bt.co.uk
  2  connect to scott
  3  identified by <password>
  4  using 'bip2d2.devenv1.bt.co.uk'
  5  /

Database link created.

SQL> 

SQL> set lin 990
SQL> column DB_LINK format a30
SQL> column HOST format a30
SQL> column USERNAME format a30
SQL> 
SQL> select DB_LINK,USERNAME,HOST from user_db_links;

DB_LINK                        USERNAME   HOST
------------------------------ ---------- ------------------------------
BIP2D2.DEVENV1.BT.CO.UK        SCOTT      bip2d2.devenv1.bt.co.uk

SQL> 
SQL> create synonym pr_last_login for scott.pr_last_login@bip2d2.devenv1.bt.co.uk;

Synonym created.
SQL>

I will now be making a RPC call to procedure pr_last_login using the DB link BIP2D2.DEVENV1.BT.CO.UK.

SQL> exec pr_last_login('E1');

PL/SQL procedure successfully completed.

SQL> 

Now, let's check the data in the table t_user_data :-

SQL> select * from t_user_data@BIP2D2.DEVENV1.BT.CO.UK;

USERID     USERNAME   HIREDATE  LAST_LOGGED_IN
---------- ---------- --------- --------------------------------------------------------------------
E1         Vijay      09-AUG-08 30-SEP-08 01.17.08.175550 PM

SQL> 

As you can see the information about last_login time has been updated/recorded.


So, herein I could successfully commit the transaction from database BIP2D2. How Oracle is then managing the transaction control, in this case ?
Shouldn't it be invoking database BIP2D2 which is supposed to "COMMIT" here.The same call, however would fail, if it involves the OUT paraneters.


Can you please explain this behaviour.

Best Regards,
Vijay

Tom Kyte

Followup  

September 30, 2008 - 9:42 am UTC

only the initiating site can commit in a distributed transaction (reason 1,234,223 I truly wish commit and rollback did NOT exist in the plsql language - along with when others, autonomous transactions and the like).


do not rely on this - what happens if you start a transaction in the primary site first - do not go down this path.

Thanks a ton....

October 03, 2008 - 2:23 am UTC

Reviewer: A reader from India

I have now got it right & fine...

It's more to do with the business functionality that one is trying to code-in...which means, under no circumstances the primary site is supposed to complete(commit/rollback) the
transaction....and thus, initiating database should always control the transactional flow....

Once again, many thanks for your contribution to Oracle fraternity....much appreciated...

Best Regards,
Vijay

Slow in Database link

November 24, 2008 - 6:02 am UTC

Reviewer: mabousaid

I have a map it reads from oracle 10g and it is very fast but when I create oracle database link to another server oracle 10g it becomes very slow and it freezes.

In this way I created db link

CREATE PUBLIC DATABASE LINK "CIS" CONNECT TO "APP" IDENTIFIED by "APP" USING 'MAKKAH'

Tom Kyte

Followup  

November 24, 2008 - 6:05 pm UTC

you have given no useful information here.


I don't know what "a map" is or does.

I don't know what the difference between the first scenario you talk of and the second is really - I don't know how you are using the database link, what are you doing with it.


Same db or different

January 24, 2009 - 6:11 am UTC

Reviewer: A reader

Hi Tom,

We are in the process of making decision, whether we should extend existing data warehouse db (10g) to include data marts or not. The obvious pros of having different instance (on different machine) is to have better control over performance (without impacting the other), independent upgrades, new installation can be 11g etc. However, there could be situations where users from DM may (sometimes) drill into DW tables.
Based upon your advise above, do you see any impact with the following approach.

1) Create new instance 11g for data marts
2) Create views in DM (11g) with DB links to DW tables(10g)
3) Let front end tool handle the drill down through views

Regards,
Tom Kyte

Followup  

January 24, 2009 - 1:29 pm UTC

what you view as "pros", I see mostly as cons

o many instances to monitor, adjust, allocate resources to, pay attention to
o having to upgrade tons of instances, instead of just one - patching patching patching.


I'm for a single database
I'll always say that, I'll always fight the creation of yet more databases...

Single db

January 24, 2009 - 6:38 pm UTC

Reviewer: A reader

Hi Tom,

Thanks for quick response and your views.
However, do you see technically any issue with this approach?

Regards,
Tom Kyte

Followup  

January 24, 2009 - 7:24 pm UTC

sorry, I thought I was clear...

Everything you see as a "pro", I see as clearly and obviously being a "con"

You will increase complexity, dependency, have more to manage, backup, monitor, tune, fix, upgrade, etc.

I see no advantage to creating a new database if the existing one has the capacity, or could be easily upgraded to have the capacity to handle the load.

Single db

January 24, 2009 - 9:11 pm UTC

Reviewer: A reader

Thanks Tom.

Agreed....

My apologies - sometimes it is not easy.. machine reached it's limit of maximum CPUs, SAN may need upgrade etc. etc.
But trying to figure out that if technically not feasible, then there is no need to even consider any other option except to upgrade it.

Tom Kyte

Followup  

January 25, 2009 - 11:10 am UTC

it is always *technically* feasible. Anything can technically be built. Software is quite flexible that way.

I run into this discussion all of the time

q: "can this be done"
a: "yes, but should you do it - that is the question we should ask"
q: "no, i just want to know 'can this be done'"
a: "in your case, no - you are no where near wanting to consider that"
q: "that doesn't answer my question"
a: "I know, I won't tell you to do something that you'll ultimately regret. Whether you *can* do something is very different from whether you *should*"


So, technically feasible - sure
Do you want to do it? Only if simplier solutions are not feasible.

Thanks

January 25, 2009 - 5:47 pm UTC

Reviewer: A reader

Hi Tom,

Thanks for the help.

Regards,

How can I find what views/synonyms use database links?

January 27, 2009 - 1:26 pm UTC

Reviewer: Kevin from Austin TX

I fear this will be simple but I'm failing miserably at finding an answer. How can I find out with a query, in a 9i database I've inherited, what views and synonyms are utilizing database links? I'm trying to untangle a web of interdependencies between 2 (or more) databases.

Thanks in advance for any assistance.
Tom Kyte

Followup  

January 28, 2009 - 3:05 pm UTC

we do not track the dependency at the database link level.

dba_synonyms does have a column for a referenced dblink.


for dba_views, you would need to use a "like" on the view text

  1  begin
  2  for x in (select owner, view_name, text from dba_views where text_length <= 32760)
  3  loop
  4    if (lower(x.text) like '%@ora11gr1@loopback%' ) then dbms_output.put_line( x.owner||'.'||x.view_name); end if;
  5  end loop;
  6* end;
ops$tkyte%ORA11GR1> /
OPS$TKYTE.V

PL/SQL procedure successfully completed.


but that'll work for 32k or less views only... (eg: most of them)

database link password

February 28, 2009 - 3:32 pm UTC

Reviewer: Matt from MA, USA

our DBA is telling "no" for database link on one of the production db p1 to another production db p2 saying that people with select catalog role on p1 can access data on p2.

is it correct that people with select catalog role can see password for database link ? If yes, what is the alternative solution ?

Thanks,
Tom Kyte

Followup  

March 03, 2009 - 10:02 am UTC

does your DBA understand the various ways dblinks can be created?

a) with a user/password hard coded, only the privileges of THAT user are conveyed, eg: you do not get your privileges on the remote site, you get the privs of the user specified in the dblink.

b) with current user, the current users credentials are used, so, if the user in the remote database has a privilege to do something, well, frankly they could just connect using sqlplus.


among others - not sure what the issue is?


and no, select catalog doesn't let anyone see the password. Ask them to demonstrate the issue, they won't be able to.

dblink password

March 04, 2009 - 7:23 pm UTC

Reviewer: Matt from MA, USA

Thanks Tom.

I asked our DBA, if there is any way he can prove the point for catalog role or otherway around to know, the password and he say it is possible,but dont know the sql at this moment.

I think I will wait for his answer, if he really has any sql to get the password, or am I asking something to risk prod env with security issue.

btw, database is Oracle 10g.

Thanks.
Tom Kyte

Followup  

March 04, 2009 - 8:55 pm UTC

select catalog role lets you see views, it does not provide access to sys.tables, you would need access to sys.link$ in older versions - and he won't have it with that role.

In current releases, the password is not stored in a readable format in sys.link$, so even if you can 'see it', it won't matter, you cannot use it.

But, you cannot see it, so the point is "not there"

Database link

March 19, 2009 - 1:27 pm UTC

Reviewer: A Reader

Hi Tom,

I am trying to create a database link using a stored procedure but getting an error ORA-01031: insufficient privileges

CREATE OR REPLACE PROCEDURE pr_create_db_link( p_user_id IN VARCHAR2,
p_password IN VARCHAR2,
p_database_name IN VARCHAR2 ) IS
g_error_msg varchar2(512);
g_sql varchar2(2000);
BEGIN
-- Create database link for source
g_sql := 'CREATE DATABASE LINK TEST.WORLD CONNECT TO '||p_user_id||
' IDENTIFIED BY '||p_password||' USING '||''''||p_database_name||'''';
EXECUTE IMMEDIATE g_sql;
EXCEPTION
WHEN OTHERS THEN
g_error_msg := RPAD(SQLERRM,512);
dbms_output.put_line(g_error_msg);
RAISE;
END;

But it works, if I replace the above as an anonymous block.

declare
g_error_msg varchar2(512);
g_sql varchar2(2000);
BEGIN
-- Create database link for source
g_sql := 'CREATE DATABASE LINK TEST.WORLD CONNECT TO '||'TEST_USER'||
' IDENTIFIED BY '||'TEST_PASSWORD'||' USING '||''''||'TEST_DATABASE'||'''';
EXECUTE IMMEDIATE g_sql;
EXCEPTION
WHEN OTHERS THEN
g_error_msg := RPAD(SQLERRM,512);
dbms_output.put_line(g_error_msg);
RAISE;
END;

Do I need additional privilege/role to create database link through a stored procedure? Please advise.


Tom Kyte

Followup  

March 23, 2009 - 9:51 am UTC

http://asktom.oracle.com/tkyte/Misc/RolesAndProcedures.html

Performance / Scalability issues with DB Links

April 14, 2009 - 3:15 pm UTC

Reviewer: Sam from OH USA

Hi Tom,

Are there any performance or scalability issues we need to consider if db links are used in an OLTP system ?

i.e. How does the link handle multiple sessions using the link simultaneously ?

Thanks

Sam
Tom Kyte

Followup  

April 14, 2009 - 4:10 pm UTC

If you are thinking of using dblinks "a lot" in an interactive OLTP application, in real time - please, please - rethink this.

First of all, why would you even consider having two databases if part of one is contained in the other. The only thing you'll get from this is massively decreased availability (the probability that one or the other is down is larger than the probability that one well managed one is). You'll have upgrade issues. You'll have performance issues (you are adding a ton of layers). You'll be doing two phase commits - which will make things slower even more (forget about the extra work to run bits of queries here there and everywhere and pull it all together).


database links are great for background stuff, moving data from OLTP to reporting, a tiny bit of really necessary replication in extreme cases - but in the background (so that if one system is down, the other keeps trucking along, so that end users don't have to wait/pay the penalty of distributed stuff).


But - it really sounds like you want a SINGLE DATABASE - ONE DATABASE.

I'm with you there

April 15, 2009 - 2:19 pm UTC

Reviewer: Sam from OH USA

Unfortunately, that is a battle that has already been fought and lost. We even showed them some one of the asktom posts that deal with this topic. The DBA team made the argument for a single database and someone (with a SQL server background) finally pulled rank on us and decided that we will have separate databases.

The issue now is that I have an application that needs to insert a few rows at a time in a remote database. The code is in pl/sql but it is part of a multi user system.

At this point my only option is to use a "shared" db link or to move the code to either java or c#.

Any suggestions ?

Thanks

Sam
Tom Kyte

Followup  

April 15, 2009 - 2:24 pm UTC

does that sqlserver guy understand that two separate databases in Oracle is ENTIRELY AND TOTALLY AND WHOLLY DIFFERENT than two databases in sqlserver?????

In sqlserver, you can have two databases in one instance (they use three layers to reference things - select * from DATABASE.OWNER.TABLE - we do not have that concept)

In sqlserver - it would make sense to use two databases in a single instance.

In Oracle - it would make sense to use two separate sets of TABLESPACES in a single instance.

Your sqlserver guy is right - in sqlserver, but not in Oracle - this is a big big - career limiting - move.

I feel so strongly about this - I'd be glad to get on the phone with you, your management team and the sqlserver guy and explain to them what a huge mistake you are making. Seriously.



You cannot move the code to java or c# (you sort of need transactional integrity here - you cannot do it in two separate transactions)


This is a huge mistake, I cannot see this happen. thomas.kyte@oracle.com



April 16, 2009 - 10:27 am UTC

Reviewer: Alexander

So Tom, does these mean if we're being forced into some terrible decision we can run it by you to see if you can talk some sense into the powers that be ;) Or is this a one time offer.
Tom Kyte

Followup  

April 16, 2009 - 11:02 am UTC

this is a one time offer as the mistake this customer is going to make is so huge.

What I know will happen:

sqlserver guy has made it so that Oracle stands zero chance of performing.
sqlserver guy does that by imposing sqlserver techniques on Oracle (the multiple database thing)
sqlserver guy will therefore 'prove' that Oracle isn't as good as sqlserver.
I can see a migration in the future.

I want to prevent about 12 months of real pain, followed by a migration.

DB Link for online huge transactions

April 28, 2009 - 8:42 am UTC

Reviewer: Arindam Mukherjee from India

Sir,

There are two Oracle 10g databases on two different servers (OS - Linux Redhat 4.0). Every day around 100 thousands records will be inserted online into two databases simultaneously. For example, there is one screen under funding module. After submission, data will be stored to Accounts module and funding module simultaneously to different tables through a PL/SQL Procedure residing in funding module. For account module, there are around 6 tables and for funding module there are maximum 3 tables. Under this circumstance, I have two options.

First option - All tables should be in one schema in one database server.

Second option - Two modules will be on different servers and database link will bridge the gap between two servers when data gets populated to two modules.

Since the transaction data volume is around 100 thousands records per day, at the end of month it could be around 300 thousands records per day, I am bit confused with database link usage.

Please help me get the right decision.

Regards,
Arindam Mukherjee
Tom Kyte

Followup  

April 28, 2009 - 10:24 am UTC

the second option should be discarded.


the first option should be rewritten, the tables need not (probably should not) be in the same schema. Division of tables, division of tables from code - very good idea.


I would definitely recommend avoiding distributed complexity (and performance impacts).

These two 'modules' want to be together.

Whatever happened to Sam of OH?

April 28, 2009 - 10:50 am UTC

Reviewer: David Weigel from Wayne, PA USA

I'm wondering how that one-time offer to Sam's company worked out, and if minds were changed. Maybe Tom can't reply because of confidentiality issues, but maybe Sam could..
Tom Kyte

Followup  

April 28, 2009 - 10:54 am UTC

never heard from them.

db_links

April 28, 2009 - 4:54 pm UTC

Reviewer: John T. from Detroit, Michigan

I had a similar problem as Sam from OH when I was asked to manage SQL Server DBAs. I decided to speak their language. It seemed to work although perhaps not technically correct.

Database = schema
Server = Oracle Instance

In which database join occurs

June 07, 2009 - 5:07 pm UTC

Reviewer: Parikh84 from Florida

Hi Tom,
Suppose I have two Database(DB1 and DB2) with a DBlink...Now,suppose there are two views(vw1 and vw2 on DB1)...Now, I create two synonym in DB2 for vw1 and vw2....Now if we do a join with the help of synonyms on vw1 and vw2 of DB1 on DB2, will the join happen on DB1 or it will take place in DB2...
Kindly help me on this.....
Tom Kyte

Followup  

June 08, 2009 - 1:31 pm UTC

it depends - it could take place in either server

use explain plan to see what the database decided to do.

passing host string as argument

June 10, 2009 - 7:59 am UTC

Reviewer: Hashmi

Dear Tom,
Oracle 10G.
I need to pass host string as arguments during creation of database links dynamically.
I have to create various links for various locations.I have created a cursor containing db link names and i have to pass them as arguments in the execute immediate statements.
For example,
for v in(select db_name from dblnk)loop
v_dblnk:=v.db_name;
execute immediate 'create public database link v_dblnk connect to usr identified by pwd using v_dblnk';
But i am getting ora-02010 error while running the procedure.

How should i overcome this problem.

Thanks
Tom Kyte

Followup  

June 10, 2009 - 2:43 pm UTC

the format of the create database link is in general:

create public database link
LINKNAME
connect to userid identified by password using
'TNSNAME'

you are using a linkname of "v_dblnk" - you are not putting the value of the variable in there - but rather the string v_dblnk. Secondly - you need to quote the tns connect string.

You need to concatenate the value in:

for v in(select db_name from dblnk)
loop
   execute immediate '
   create public database link ' ||
   v.db_name || '
   connect to usr identified by pwd using ''' || 
   v.db_name || '''';
end loop;



and you need to decide if you need to check for sql injection issues (google sql injection if that term means nothing to you)

June 11, 2009 - 2:51 am UTC

Reviewer: Hashmi

Dear Tom,
I need to insert records from remote locations.For that I have done this:
db_lnk varchar2(100);
for v in(select db_name from dblnk)
loop
execute immediate '
create public database link ' ||
v.db_name || '
connect to usr identified by pwd using ''' ||
v.db_name || '''';
insert into usr.tab1 select * from tab1@'''||v.db_name||'''
end loop;
But I am getting ORA-01729: database link name expected
error.
If i use a variable like
db_lnk:=v.db_name;
insert into usr.tab1 select * from tab1@db_lnk;

It throws table or view does not exist.

All I want to do is achieve a functionality where I can dynamically create database links one by one through a loop and insert data from those links in the loop.

Thanks

Tom Kyte

Followup  

June 11, 2009 - 8:47 am UTC

if you dynamically create something

in a block of code

and want to reference that something

in that same block of code

you must reference it dynamically as well - because the block of code cannot compile otherwise.


Do you by any chance have an experienced pl/sql developer nearby that can mentor you - some of this is fairly basic stuff - a mentor is the best way (in my opinion) to learn.


I see a lot of problems in your code.

first the create will commit. If your code fails halfway through - half of the inserts will be committed and the other half will not have happened. If you try to restart your code, it will fail immediately since you don't deal with "database link already exists". I can see that as the next question after I show you how to do this with a dynamic insert (hence - my suggestion of "mentor" - to head that probable outcome off...)

ops$tkyte%ORA10GR2> create table t
  2  ( db_name varchar2(40), db_connect varchar2(40) );

Table created.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> insert into t values ( 'ora10gr2@loopback', 'ora10gr2' );

1 row created.

ops$tkyte%ORA10GR2> commit;

Commit complete.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> drop table t2;

Table dropped.

ops$tkyte%ORA10GR2> create table t2( txt varchar2(80) );

Table created.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> declare
  2          db_link_exists exception;
  3          pragma exception_init( db_link_exists, -2011 );
  4  begin
  5          for x in ( select * from t )
  6          loop
  7                  begin
  8                          execute immediate '
  9                  create public database link ' ||
 10                  x.db_name || '
 11                  connect to ops$tkyte identified by foobar using ''' ||
 12                          x.db_connect || '''';
 13                  exception
 14                          when db_link_exists
 15                          then
 16                                  dbms_output.put_line( 'skipping create of ' || x.db_name || ' already exists' );
 17                  end;
 18
 19                  execute immediate 'insert into t2@' || x.db_name ||
 20          '( txt ) select username from all_users where rownum <= 5';
 21          end loop;
 22  end;
 23  /

PL/SQL procedure successfully completed.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> select * from t2@ora10gr2@loopback;

TXT
-------------------------------------------------------------------------------
SYS
SYSTEM
OUTLN
MGMT_VIEW
MY_USER

ops$tkyte%ORA10GR2> @test
ops$tkyte%ORA10GR2> set echo on
ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> drop table t;

Table dropped.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> create table t
  2  ( db_name varchar2(40), db_connect varchar2(40) );

Table created.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> insert into t values ( 'ora10gr2@loopback', 'ora10gr2' );

1 row created.

ops$tkyte%ORA10GR2> commit;

Commit complete.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> drop table t2;

Table dropped.

ops$tkyte%ORA10GR2> create table t2( txt varchar2(80) );

Table created.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> declare
  2          db_link_exists exception;
  3          pragma exception_init( db_link_exists, -2011 );
  4  begin
  5          for x in ( select * from t )
  6          loop
  7                  begin
  8                          execute immediate '
  9                  create public database link ' ||
 10                  x.db_name || '
 11                  connect to ops$tkyte identified by foobar using ''' ||
 12                          x.db_connect || '''';
 13                  exception
 14                          when db_link_exists
 15                          then
 16                                  dbms_output.put_line( 'skipping create of ' || x.db_name || ' already exists' );
 17                  end;
 18
 19                  execute immediate 'insert into t2@' || x.db_name ||
 20          '( txt ) select username from all_users where rownum <= 5';
 21          end loop;
 22  end;
 23  /
skipping create of ora10gr2@loopback already exists

PL/SQL procedure successfully completed.

ops$tkyte%ORA10GR2>
ops$tkyte%ORA10GR2> select * from t2@ora10gr2@loopback;

TXT
-------------------------------------------------------------------------------
SYS
SYSTEM
OUTLN
MGMT_VIEW
MY_USER




Sys is powerless

July 08, 2009 - 10:44 am UTC

Reviewer: A reader

Hi tom,
I logged in as SYS and tried to drop a private dblink owned by another user.
It says
ORA-02024: database link not found

Though I do see it in dba_db_links.

How to make this happen ?
Tom Kyte

Followup  

July 08, 2009 - 3:45 pm UTC

database links are "special", there is no way to address them with a schema.

The implied/inferred schema is always the current user OR public.

Since you cannot specify the other user in the database link - you cannot drop it.


think about it - since you cannot specify a schema on a dblink (ever), what would happen if you had five users each with a database link named "foobar" and sys issues

drop database link foobar;


what database link could it/should it/would it drop?

Answer: unknown - we don't know what the intent was, we don't know what link to drop, we cannot drop anything

sys is powerless : DB version is 9208

July 08, 2009 - 10:44 am UTC

Reviewer: A reader


Sys is powerless

July 08, 2009 - 5:26 pm UTC

Reviewer: A reader

Thanx for the explanation.

At least Sys could have this special power to do.

Looks like this is the only thing Sys cannot do to other user objects.

Question :--
Why you cannot specify a schema on a dblink ?
If we are able to qualify other db objects with its owner why not a DB link . May be then Sys can do the drop.




Tom Kyte

Followup  

July 08, 2009 - 7:38 pm UTC

because a database link is like a hostname,


create database line scott.foo.bar.hello.world .........;

is valid - scott is not a schema, there is no way to discern what a schema would be in that context.


You should never ever be using sys by the way, create you OWN account

Sys is powerless

July 09, 2009 - 10:04 am UTC

Reviewer: A reader

Tom Thanx for your feedback.

May be we can put this as an enhancement request or a nice to have feature.

Now to drop the dblink we would need to know the password of the schema or change the password ,drop dblink and then revert the password thru identified by values if we dont know the password.

That is too much of work if we have to drop a lot of private db links.

It is a common requirement to give production copy for Qa purpose and we then clean up those dblinks and give it to QA

Thoughts ?
Tom Kyte

Followup  

July 14, 2009 - 2:50 pm UTC

think about it - there is no place for the username


scott.foobar.hello.world@overthere@andoverhere

is a valid database link name.


You do NOT need to know a schema password to connect as another user, not for many releases. you have the "connect through" privilege since 8i.

http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:83012348058#408884400346292168

More on ORA-02064

August 06, 2009 - 4:42 pm UTC

Reviewer: Bob from Knoxville, TN

We are looking at the option of having a job submitted on the remote server to avoid the 2064 problem. If we pass parameters to and from the remote job using a table, can we use a trigger on the table to submit the job when the data is inserted?

Or, can we take it one step further - what about having the trigger execute the procedure directly? Or does this bring us back to the 2064 problem?
Tom Kyte

Followup  

August 07, 2009 - 8:38 am UTC

you would have to explain what is CAUSING the ora-2064 first.


August 17, 2009 - 4:00 am UTC

Reviewer: James Mattew from Oklahama,USA

Hi Tom,

I have a question for you ? I have two databases supposedly ORCL and ORCL1 and I need to migrate the data from ORCL to ORCL1 and both these databases are rhost connected with the dblinks connected etc .. but I want to connect to the database ORCL from a third box (say NEW) which doesn't have oracle and want to migrate ORCL to ORCL1 .. I need the imp/exp files of ORCL etc all on this NEW box and need this to be fired from this box to ORCL1 via ORCL

Note : All the three boxes are connected in the same VPN and we can have the boxes connected using rhosts/rsh/rcp

Is this do able ? Any help is appreciated

Thanks

Tom Kyte

Followup  

August 24, 2009 - 8:49 am UTC

you will have to install the oracle client on the "new" box if you want exp/imp to be present on the "new" box


or, export the file system of "new" box and mount it on ORCL, exp there to the mounted filesystem

Ora-12640

August 19, 2009 - 6:51 am UTC

Reviewer: ashish from INDIA

Hi Tom,

I am getting Ora-12640 errors in my sqlnet.log. I am having oracle 10.1.0.2 with windows.

Present value of SQLNET.AUTHENTICATION_SERVICES is (NTS) and I can not set it to NONE. I have windows users who access/login the database.

Also, this error get resolved when restarting the server. But appears anytime again after 3-4 days.

Can you suggest what can be the problem, which areas should I search to find the exact cause of this error.

Regards
Ashish

from db1 to db2

August 21, 2009 - 3:04 am UTC

Reviewer: Gayatri from India

The posts on this page are very useful. Thank you. Pl check my problem as below.

I have two databases db1 and db2. Day end I need to replicate from db1 to db2. I have plsql stored procedure to do this for me. Now, I had to set up a new box for these servers.
Data from old to new servers is ported using Disk dump.

All such procedures having dblinks are not compiling (hanging forever). I need to kill the hanging procedure explicitly to come out.
My old servers are still working fine....
Pl throw light on this....
Tom Kyte

Followup  

August 25, 2009 - 8:45 am UTC

you know, replication is a feature the database has provided for longer than I've worked at Oracle (I joined in 1993). Why someone would write it in the 21st century escapes me.

It sounds like your newly created servers have their database links created incorrectly and tcp/ip is not timing out. Have you even tested to see if the links work a little bit?

September 02, 2009 - 1:07 am UTC

Reviewer: Ashish

I am getting Ora-12640 errors in my sqlnet.log. I am having oracle 10.1.0.2 with windows.

Present value of SQLNET.AUTHENTICATION_SERVICES is (NTS) and I can not set it to NONE. I have
windows users who access/login the database.

Also, this error get resolved when restarting the server. But appears anytime again after 3-4 days.

Can you suggest what can be the problem, which areas should I search to find the exact cause of
this error.

Regards
Ashish
Tom Kyte

Followup  

September 02, 2009 - 10:29 am UTC

$ oerr ora 12640
12640, 00000, "Authentication adapter initialization failed"
// *Cause:  The function specified in the authentication table entry for the
//          service failed.
<b>// *Action: Enable tracing to determine the exact error.
</b>

DB Replication

September 08, 2009 - 5:14 am UTC

Reviewer: Gayatri from India

My db links are working fine. The same statements which are inside the Stored procedures are working from sql prompt. Its surprising that the procedures don't compile.
Pl check below my old post for better understanding.
Rgds



The posts on this page are very useful. Thank you. Pl check my problem as below.

I have two databases db1 and db2. Day end I need to replicate from db1 to db2. I have plsql stored
procedure to do this for me. Now, I had to set up a new box for these servers.
Data from old to new servers is ported using Disk dump.

All such procedures having dblinks are not compiling (hanging forever). I need to kill the hanging
procedure explicitly to come out.
My old servers are still working fine....
Pl throw light on this....

Followup August 25, 2009 - 8am US/Eastern:

you know, replication is a feature the database has provided for longer than I've worked at Oracle (I joined in 1993). Why someone would write it in the 21st century escapes me.

It sounds like your newly created servers have their database links created incorrectly and tcp/ip is not timing out. Have you even tested to see if the links work a little bit?

data base link

October 23, 2009 - 5:10 am UTC

Reviewer: Nazmul Hoque from Bangladesh

Dear Tom.

I am connecting my database below tnsnames.ora in my lan connection, Now i want to connect the same from a VPN, What change required in the below to connect server(database) for VPN

GASLDATA =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = GASLDHK)(PORT = 1521))
(CONNECT_DATA = (SID = GASLDATA))
)

Please let us know if any solution is there.

Thanks in advace
Tom Kyte

Followup  

October 23, 2009 - 2:23 pm UTC

Umm, when you vpn your machine into another network, the GOAL of the vpn software is to prevent the two networks from seeing eachother.

When you VPN into work for example, your local network is "gone, not visible"

that host - gasldhk - unless it exists on the network you vpn'ed into, it doesn't exist.

work in vpn

October 24, 2009 - 11:56 pm UTC

Reviewer: Nazmul Hoque from Bangladesh

Hi Dear,

I have two local lan, lan1 and lan2. Lan1 have oracle server 8.1.7 and user under lan1 can connect oracle easily. lan1 and lan2 is connect through VPN, user of Lan1 and Lan2 both can share there easily and can server (lan1) also. now user of lan2 wants to user oracle from server lan1(gasldhk), for this what change required fOR LAN2 user to connect database IN TNSNAMES.ORA

please advise.
Tom Kyte

Followup  

October 26, 2009 - 1:58 pm UTC

there would be no change.


If they can ping it, they can use sqlnet to get to it.

so, can they ping that host - or telnet to it, or whatever - use any other tool on the planet that uses tcp ip and ensure that host name is known to the users on "lan2"

connect in a VPN

October 27, 2009 - 5:01 am UTC

Reviewer: Nazmul Hoque from Bangladesh

Thanks, now i am able to connect after change the HOST = GASLDHK to HOST=192.168.1.100,

Thanks Once again


My Insert queries are very slow over remote DB Link

November 16, 2009 - 4:00 am UTC

Reviewer: A reader

Tom I have a procedure pushing data as inserts over a remote DBLInk.
Insert into test@remoteDBlink values(........);

My procedure has been working fine from last 2 months but off-late has started taking much more time and has become a bottleneck.

Surprisingly, when I am using prefix schema name instead of remote dblink, same procedure works fine.
insert into scott.test values(...........);

Both of my schema's are on same database server for now, but my customers plans to move it to another box. Hence I I guess remote dblink must be used.

Are their any obvious performance hits with remote dblink or am I missing on any setting on my new database server.


please help...
Tom Kyte

Followup  

November 23, 2009 - 9:29 am UTC

... Surprisingly, when I am using prefix schema name instead of remote dblink,...

surprisingly? I'm surprised someone would say that.

Analogy:

with dblink: I'm in Virginia, I have to call someone in California to tell them to do something. In order to do that, I have to look up their phone number, pick up the phone, dial them, wait for them to answer, and then tell them what to do.

without dblink: I'm in Virginia, the person I need to tell what to do is standing next to me. I turn to them and speak.


first suggestion, enable tracing - do some diagnostics yourself. What takes long? Does it take long to establish a session to the remote database (just try select * from dual@remote in a new sqlplus session and see how long that takes a) the first time and b) the second time - the first time connects). Is it possible the remote table has a unqiue constraint on it and you are getting blocked? How is that network between the two?




And most importantly, ask yourself "if I have to insert FREQUENTLY into a remote table as part of a distributed transaction, Have I lost my mind? I really meant to have A SINGLE DATABASE" - distributed complexity should be avoided at all costs - your availability is really low in that environment, your performance will always be impacted by the performance of the remote site.


do you need to do this in real time? Instead of doing it while the end user waits, can you do it in the background shortly after they commit? (eg: use the builtin stuff to share data - streams, materialized views, whatever)

How to revoke access from a public database link

November 26, 2009 - 12:07 pm UTC

Reviewer: Juan Carlos from Bolivia

Hi Tom, nice to talk you, how can I revoke access from a public database link.

because if I connect only with create session and alter session privileges, I can get full access to other tables through public database links, because they were created specifying the user and password.

All users uses this link , and not all users are created in both database. Do you have some suggestion?, please

Thank you:)
Tom Kyte

Followup  

November 28, 2009 - 1:20 pm UTC

drop the public database link and use private database links for the users that should have access to it.

drop the public database link, create a new account with a private database link, create views of the remote objects you want to expose, and grant on just the views.


drop the public database link, have the remote system create a new account with just the privileges you want everone to have, and recreate the public database link using that new identity.


etc - variations on the above themes.

December 08, 2009 - 3:07 pm UTC

Reviewer: A reader

Thank you Tom, but I think access to database links, should requiere a role in the future.
:)
Tom Kyte

Followup  

December 10, 2009 - 1:22 pm UTC

capability already exists.

create a schema.
create a PRIVATE database link.
create views.
grant on views.

December 11, 2009 - 7:53 am UTC

Reviewer: A reader

Thanks Tom you are right, but a role or privilege will help anyway to improve security. Most people didn't knew about this, they supposed they must have enabled other role than connect to access data through database links.


Tom Kyte

Followup  

December 11, 2009 - 8:08 am UTC

why would they suppose that?

"create PUBLIC database link" <<<== PUBLIC, public... *public*


versus

"create database link" <<<=== not public


and if an application went production because an entire DBA team and development team didn't know this, then I say an application that was never reviewed critically just went production.




most people do not know that

a) triggers should be avoided, used as a last resort
b) how to use triggers when they do use them
c) that when others not followed by a raise is almost certainly a bug
d) that autonomous transactions are evil, pure and simple, when used anywhere other than an error logging routine
e) that bind variables are in fact something to use, not avoid

and so on. The list of what most people do not know is infinitely long and can only be corrected by.....

well, educating I suppose.

Export database link

December 20, 2009 - 11:36 am UTC

Reviewer: A reader

Tom,
Recently I realized that database links can create a potential security situation. In Orcale 10g, it is possible to use data pump export to export just the database links in a database. The resulting export file can be imported into any database and I can connect to the remote database with the user ID of the "connect to" user without ever having a need to know that user's password.

This seems like a very easy way to circumvent the username/password requirement for one database user account at least. I would suggest that export (whether conventional or data pump) should be modified in such a way that links should be created but should require the password of "connect to" user on first use or during import process itself.

Granted that it would require some elevated level of access to the database which has database links, it is possible nonetheless.

What are your thoughts on this?

Thanks...
Tom Kyte

Followup  

December 21, 2009 - 1:14 pm UTC

umm, did you realize that export (data pump or otherwise) can be a security issue.

If you export the data from a database
and you give someone access to that file.....
they have your data


Anytime you take anything out of the database, you have to be aware of

a) whom has the ability to take it out.

(someone that can export database links can export the entire database, they can export the user accounts, they could import this file (no data, just users) and then run a password cracker against it with rainbow tables to speed it up.

b) who has access to the export dump files.

Since they will have 100% access to *everything* in that file. *everything*. No need for a database link to a remote system, they have the *local* system.


11g Release 1 and up allows you to encrypt a dmp file, so someone would have to have the keys to use it.


My thoughts on this are.... No, this is not an issue with what export does (hey, did you know that if you take a backup of your database..... just replace export with backup).

You need to physically secure your data - period.

Export database link

December 21, 2009 - 7:48 pm UTC

Reviewer: A reader

I think I did not explain the situation properly. My production database is PRDLOC. This database is secure with all kinds of security checks in place.

A business associate connects to my database using database link on their database PRDREM. I have created a user ABC on PRDLOC which has access to some protected data. PRDREM uses this user account ABC to access the protected information over database link.

PRDREM gets compromised. An attacker managed to export just the database link definitions from PRDREM. Now the attacker can connect to PRDLOC and get hold of protected data.

a) The attacker did not get hold of PRDLOC database export or backup files.
b) The attacker did not crack the passwords of PRDLOC database using rainbow tables which can potentially take months.
c) The attacker did not reverse engineer the export files or data files, which again could have taken several days.
d) The attacker did not sniff any network data.

The attacker still had access to data very quickly because the username and password were pre-filled for him by Oracle.

Oracle has created advanced security option keeping in mind that one layer of security can always be compromised. TDE protects my data in use, network security protects my data over the wire, encrypted exports/backups again protect exports/backups at rest.

Oracle does not even allow creating a database link with substituting "identified by values <password hash>" instead of "identified by <password>". Oracle has removed the password hash column from dba_users in 11g.

Clearly someone at Oracle is thinking that plain physical security of database is not enough.

I still feel that allowing database link to be created without asking for a password is a security hole. Sorry that you disagree.

Thanks...
Tom Kyte

Followup  

December 23, 2009 - 7:09 am UTC


If you allow someone to attack that database, it is not any different than you allowing them to attack production

If you allow someone to attack that database, it is not any different than you allowing them to attack production - have you thought about that. I'll open with that and close with that thought:


I understood fully what you meant, entirely, it is again - not a security thing regarding export/import to me.

If you have a production database and are giving someone a FULL EXPORT OF IT, you might as well give them your backups (in fact, I would say - GIVE THEM the backups, using export is a silly waste of your time and your resources).

If you give them that export, you give them everything - no kidding, isn't that obvious?

a) no, the attacker had access to something even better, a full copy of production - like a restored backup, and YOU gave it to them, not us.

b) not with rainbow tables, with those, that would take seconds at most to find popular passwords. Months - forget about months, minutes on a laptop.

c) no one on the planet has to reverse engineer anything (and things only need to be reversed once - once one person did that, it is milliseconds for everyone else - please think about that...). Export is a file format you have a tool to use against already, there is no reversing necessary.

d) didn't have to - YOU GAVE HIM ACCESS TO EVERYTHING.

The probably as I see it is your weak security that allows PRDREM to get compromised. Just as it would be if you let them get at PRDLOC.


Your data (database links, tables, everything) is precious, it is your job to ensure the correct physical security is IN PLACE at all times.


... Oracle has created advanced security option keeping in mind that one layer of
security can always be compromised. ...

but you know what, if you DON'T USE IT, it doesn't do anything. Just like all security practices. If you take your backups and give them to a third party, the same thing would be true (encrypt them and it isn't). You have given your entire database to someone else and that someone else isn't practicing any sort of physical security. What we are to do? Really? Honestly.


... I still feel that allowing database link to be created without asking for a
password is a security hole. Sorry that you disagree.
....

how about creating a user?
how about creating a public synonym?

You know what - it did ask for a password, the password of a DBA on the target database - someone that knows what they are doing (presumably).

It does seem you are aware of the issue - if you haven't done something about it (eg: the best bet would be to export ONLY THAT WHICH IS NECESSARY TO BE EXPORTED - the concept of "least", like "least privileges")


I see this as being no different then us creating a table in another schema other then the importer - all without asking for your permission. You already GAVE it to us, you asked us to do this.

A full export/import is very similar to a cold backup in noarchivelog mode. A complete and total point in time view of the data.

If you allow someone to attack that database, it is not any different than you allowing them to attack production - have you thought about that. I'll open with that and close with that thought:

If you allow someone to attack that database, it is not any different than you allowing them to attack production

views

December 23, 2009 - 9:29 pm UTC

Reviewer: A reader

Tom:

Quick question on using tables over db links.

Do you recommend using views instead of remote table for queries:

--I usually do this
db1>select a.*,b.*,c.* from table1@db2link, table2@db2link, table3@db2link where....

--Is this much better

db1>create view table1 as select * from table1@dblink
db1>create view table2 as select * from table2@dblink
db1>create view table3 as select * from table3@dblink

db1>select a.*,b.*,c.* from table1, table2, table 3
where.....


Would this have any impact on performance (shared pool,buffer cache, data dictionaary) in any way since you mentioned the metadata will be local?

I have so many SQL queries that use links and if this greatly improves stuff I will implement it even though we have an extra object and if you change the table you have to recreate the view.
Tom Kyte

Followup  

December 31, 2009 - 2:28 pm UTC

the shared pool and dictionary cache, but not the buffer cache, will have a tiny bit of information in it using the view that it might not otherwise.

But if you ask me, the benefit of the view here outweighs any possible negatives.


It would not necessarily "greatly improve stuff", I like it because it does import the metadata locally so things that query all_tab_columns - will see it, applications that expect to work on tables (and use the metadata about them) will work with it, compiling plsql and other views that reference the remote objects via the view will benefit from the local metadata and so on.

views

December 23, 2009 - 9:29 pm UTC

Reviewer: A reader

Tom:

Quick question on using tables over db links.

Do you recommend using views instead of remote table for queries:

--I usually do this
db1>select a.*,b.*,c.* from table1@db2link, table2@db2link, table3@db2link where....

--Is this much better

db1>create view table1 as select * from table1@db2link
db1>create view table2 as select * from table2@db2link
db1>create view table3 as select * from table3@db2link

db1>select a.*,b.*,c.* from table1, table2, table 3
where.....


Would this have any impact on performance (shared pool,buffer cache, data dictionaary) in any way since you mentioned the metadata will be local?

I have so many SQL queries that use links and if this greatly improves stuff I will implement it even though we have an extra object and if you change the table you have to recreate the view.

Database Links

February 09, 2010 - 11:32 pm UTC

Reviewer: Hariharan from Chennai, India

Hi,

Good Day.

We have a database link connecting two databases Database A and Database B. Database B uses database link to retrieve a set of rows from a view using a select statement. Number of rows varies with minimum of 1000 records on a day and goes upto a million or two on another day.

Occassionally we have an issue of CONNECTION LOST when data gets transferred and my DBA recommends not to use Database Link as he thinks that this is due to Database Link and we keep telling him that it cannot be due to database link and it is due to some network issues. Now, my question is as follows:

a) In future, is there anyway we can invoke NETSTAT from inside Oracle database whenever this issue occurs?
b) If the answer is NO for the above question, is it possible to find out why this error occurs? We checked ALERTLOG and user trace files, but seems to be no useful information available.
c) If the answer is NO for the above 2 questions, can you guide me to trap the root cause of this issue?

Version: Oracle Database 10.2.0.2
OS: Solaris 10

Thanks Tom

Hari
Tom Kyte

Followup  

February 15, 2010 - 3:05 pm UTC

a) what would that do for you? You could write a java stored procedure - but I don't see what that would do for you.

b) you can enable tracing for most any error (enable an event to cause a trace file to be generated upon a specific error), support will guide you through the steps.


Checking db_link status

March 29, 2010 - 5:04 am UTC

Reviewer: Ulfet

Hello Tom.
I need your help as usual:)
I want to check db_link status. (I have created job and scheduler).

But firstly let me write you that my below script works abnormal.


DECLARE
str VARCHAR2 (2000);
tmp VARCHAR2(100);
x NUMBER;
BEGIN
DBMS_OUTPUT.put_line ('Exists DB_LINK(s) on DB');
DBMS_OUTPUT.put_line ('==========================================');

FOR c IN (SELECT db_link FROM dba_db_links where rownum <5)
LOOP

-- SELECT COUNT (1) INTO x FROM dual@dbtest_dbprod;
-- SELECT COUNT (1) INTO x FROM DUAL@||c.db_link;

--raise_application_error(-20001,'Too Many Database Links in use');

str := 'SELECT COUNT (1) FROM DUAL@'||c.db_link;

execute immediate str into tmp;
IF tmp <> 1 THEN
DBMS_OUTPUT.put_line (c.db_link || ' -> db_link does not work!!!');
ELSE
DBMS_OUTPUT.put_line (c.db_link || ' -> db_link works!');
END IF;

END LOOP;


EXCEPTION
WHEN OTHERS THEN
raise_application_error(-20001,'Exception - '||SQLCODE||' -ERROR- '||SQLERRM);
END;

DBMS_OUTPUT.put_line ('==========================================');

END;


I have 11 db_links which 3 of them are not work, but status on dba_objects is VALID.

questions:
when using: FOR c IN (SELECT db_link FROM dba_db_links where rownum <5) it works normal but when use only SELECT db_link FROM dba_db_links it does not work, raise_application I know the reason, relation init.ora parameter file which means too many open db_links.

I know which db_links do not work (I have tested all db_links to know which is an available) and when I use it in cursor it works :
FOR c IN (SELECT db_link FROM dba_db_links where db_link not in ('test1link','test2link','test3link'))
loop
...
ed loop;



how can I show which db_link(s) does not work?

I have meant :

FOR c IN (SELECT db_link FROM dba_db_links)
....
--One exception I found (too many open db_links), but what about how can I know which db_links exactly does not work


Can you correct my script?

I need to write script checking db_link`s status and which of them does not work and reason why does not work.

Thank you in advance.
Tom Kyte

Followup  

April 05, 2010 - 9:48 am UTC

EXCEPTION
   WHEN OTHERS THEN
      raise_application_error(-20001,'Exception - '||SQLCODE||' -ERROR- 
'||SQLERRM);
END;
  
   DBMS_OUTPUT.put_line ('==========================================');

END;


I hate your code
http://asktom.oracle.com/pls/asktom/asktom.search?p_string=%22i+hate+your+code%22

read that for the reason why.



I have no idea, none, what you mean by "does not work".

My car won't start.

when you can tell me why my car won't start, I'll be able to tell you what "does not work" means.


I have no idea what you are really trying to do here.

db link

April 05, 2010 - 10:39 am UTC

Reviewer: A reader


DB LINK DOWN

August 31, 2010 - 1:14 am UTC

Reviewer: Som Debnath from India

Hello Tom,
Recently, I have got a problem while accessing data from a remote database over DB LINK. When I am trying to get the table data,the select query got hanged and it didn't return anything in 2 days also. The query is:-

select 1 from DUAL@DB_LINK_REMOTE;

I've no clue why this is happening. Please give some light on this.

Thanks,
SomD

question on DBlink

January 15, 2011 - 12:18 am UTC

Reviewer: john

I create a DB link from local db-A to a target DB-B. How come this db link gets connect to a user (XXX) on target DB-B? andof course the user Name (XXX) is already existed in DB-B
Tom Kyte

Followup  

January 23, 2011 - 2:59 pm UTC

you don't say how you created the database link, but it sure sounds like you created it with 'connect to XXX identified by YYY' - meaning, you told us what user to connect as.

Process slow

January 15, 2011 - 12:20 am UTC

Reviewer: john

TOM:
Iam having an issue that procedure call executed really slow where underline code trying to convert from Blob to Clob. What can i do? Thanks


Tom Kyte

Followup  

January 23, 2011 - 3:01 pm UTC

you can

a) define what you mean by "slow", perhaps what you think is slow is really light speed and you need to reset your expectations.

b) tell us about how much data you are dealing with - 5 bytes? 5 mbytes? 5 gbytes? 5 tbytes? it would make a difference.

c) show us HOW you are converting the data - are you doing it yourself byte by byte or what? I mean there are api's to do this - how are you doing it

Accessing specific objects through DBLINK

March 01, 2011 - 7:23 am UTC

Reviewer: Sudeep from Hyd, India

Hi Tom,

I have a specific requirement.
We have two seperate applications running on seperate databases in seperate locations (let me name the databases as DB_loc1 and DB_loc2)

Currently we have a scenario in which DB_loc1 needs to access some specific tables of DB_loc2(NOT ALL) and vice versa.

I tried to google it out to see if we can access only some specific DB objects on the remote DBs, but in vain.

The only approach that i see is to create seperate schemas on both the DBs with grants for the specific tables only from the main schema. But this seems a bit heavy from the maintainence side. Too much of a workaround.

Can you suggest any approach to have a limited but direct aceess to the remote schema's objects.
Tom Kyte

Followup  

March 01, 2011 - 12:29 pm UTC



You control access to objects via grants, of course you can limit access to specific objects - you would just GRANT on the objects you wanted to have access to.



... But this seems a bit
heavy from the maintainence side. Too much of a workaround. ....


how the HECK is this a workaround????? Seriously??? think about what you just said here - how is this a workaround.

This is in fact the correct and proper approach to the problem. "A bit heavy", sorry if security and limiting access is a "bit heavy" for you - but think about it - you have to list the objects SOMEWHERE. That is what this schema will do for you.


DB Link

March 08, 2011 - 9:09 am UTC

Reviewer: Diana from Chicago, USA

Hi Tom,

Thank you in advance for your time. Your help is priceless.
I have a question related to DB Links.
I created 2 database links. " DIANA_REG" and “DIANA_JDBC”.
---------------------------------------
CREATE DATABASE LINK " DIANA_JDBC"
CONNECT TO "ABC" IDENTIFIED BY "XYZ"
USING
'jdbc:oracle:thin:ABC/XYZ@ramxtxus011:1521:DIANA'
;
CREATE DATABASE LINK " DIANA_REG"
CONNECT TO "ABC" IDENTIFIED BY "XYZ"
USING
'(DESCRIPTION =(ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST =ramxtxus011)(PORT=1521)))(CONNECT_DATA=(SID=DIANA)))';
---------------------------------------
The "DIANA_DIANA_REG" works fine.
The “DIANA_DIANA_JDBC” has 'jdbc:oracle:thin:ABC/XYZ@ramxtxus011:1521:DIANA' in the ‘using’ clause and gets an error: ORA-12154: TNS:could not resolve the connect identifier specified
I also created a Java program and tested 'jdbc:oracle:thin:ABC/XYZ@ramxtxus011:1521:DIANA'. It works fine from my Java program,.
---------------------------------------
QUESTION: Is it possible to create a valid DB link with 'jdbc:oracle:thin:ABC/XYZ@ramxtxus011:1521:DIANA' in the ‘using’ clause and get it to return data from the target database DIANA?
---------------------------------------
Thank you,

Diana

Tom Kyte

Followup  

March 08, 2011 - 1:01 pm UTC

that is a jdbc connection URL, it cannot be used in a database link.

get rid of the jdbc junk at the front of that - the connect string for us follows the @


create database link xxxx connect to u identified by p
using '//hostname:port/service';


make sure you have EZCONNECT as a naming method in your servers sqlnet.ora file

Create Oracle Database Link Review

March 15, 2011 - 9:26 am UTC

Reviewer: Rahinur Rahaman

Create Oracle Database Link requires some planning and preparation. In this article, this planning and preparation is defined step by step.
http://www.rahinur.com/create-oracle-database-link/
Here I just want to add some restriction while create oracle database link:
Restriction: You cannot create an Oracle database link in another user’s schema, and you cannot qualify dblink with the name of a schema. Periods are permitted in names of Oracle database links, so Oracle Database interprets the entire name, such as john.misbdlink, as the name of a database link in your schema rather than as a database link named misdblink in the schema john.

Thanks!

Tom Kyte

Followup  

March 15, 2011 - 9:31 am UTC

sorry, but that article doesn't really tell you anything the documentation didn't already tell you - only with more information (the docs tell you more).

http://docs.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_5005.htm#SQLRF01205

and funny enough, we seem to have used the same graphic artist?

I don't mind anyone posting a link to external relevant material - but you should make sure first that

o it actually provides value. It is beyond the documentation. This isn't.
o it doesn't actually borrow images from the documentation.

Confused about v$dblink vs v$session

May 06, 2011 - 1:00 pm UTC

Reviewer: Dana from Phoenix, AZ USA

I am a bit confused about database link resources and connections. Oracle docs indicate it is a good practice to "close" links when they are infrequently used.
That part makes sense. When querying v$dblink there is no activity, but when I look at v$session there is an inactive session. Is there a way to completely disconnect from the remote database without terminating the session on the local database? Or does it matter? Sample of query/view in "remote" db:
SQL> select db_link,owner_id,logged_on,open_cursors,in_transaction,update_sent from v$dblink;

no rows selected

SQL> select username,status,machine from v$session where username='COMMON_SEQ_MAN';
USERNAME        STATUS       MACHINE
--------------- ------------ ------------
COMMON_SEQ_MAN  INACTIVE     remoteserver


And the code on the "local" db is:

SELECT SEQUENCE_NAME_ID.NEXTVAL@REMOTE_DB.WORLD FROM DUAL;


Once I exit the session on the local db, the remote db no logner shows a connection which is expected.

Local DB:
SQL> exit


And the remote db no longer shows any session:

SQL> select username,status,machine from v$session where username='COMMON_SEQ_MAN';

no rows selected


Thanks for your time.
Tom Kyte

Followup  

May 06, 2011 - 2:37 pm UTC

quote from the documentation:

<quote>
V$DBLINK describes all database links (links with IN_TRANSACTION = YES) opened by the session issuing the query on V$DBLINK. These database links must be committed or rolled back before being closed.
</quote>

V$dblink is for *your* sessions database links only.


Also - the act of closing a database link is done by the person that initiated it - NOT by you outside of that session. Meaning - the session on the "remoteserver" is the only one that can close that database link - you cannot.


And - if you just have one of them, it is not a big deal, you do not need to have it closed.


Wow, they select a sequence over the dblink. Why??? what is the goal here? If they are trying to achieve "global uniqueness" - they should either

a) use sys_guid()
b) recreate the sequence on both sites - on one site they would:

create sequence seq_name start with CURRENT_MAX_VAL increment by 10;

and on the other

create sequence seq_name start with (CURRENT_MAX_VAL+1) increment by 10;



that would allow for up to 10 sites to generate unique numbers.

Correct

May 06, 2011 - 3:29 pm UTC

Reviewer: Dana from Phoenix, AZ USA

Yes, the global unique is the purpose. And yes, it is a inhibitor for many things: scalability, fault tolerance, manageability and more.

And I agree with the alternatives, and suggested the alternatives. Win a few, lose a few.
Tom Kyte

Followup  

May 09, 2011 - 6:57 am UTC

but some battles are bigger and more important than others. This is a pretty humongous battle.

db link

May 08, 2011 - 9:54 pm UTC

Reviewer: A reader


I agree

May 15, 2011 - 12:07 pm UTC

Reviewer: Dana from Phoenix, AZ USA

It is a battle. I lost that one, and still wage the war on lack of bind variables. I win the bind variable battles, so I consider it better at the end of the day.
The particular sequence over a link battle had the mitigating factor of being fewer than one hundred calls per day. The bind variable battle is hundreds per second. Or that's my rationalization. Sigh.
Tom Kyte

Followup  

May 18, 2011 - 3:02 am UTC

I win the bind variable battles, so I consider it better at the end
of the day.


I concur!


gettting host date from the remote database

June 21, 2011 - 3:23 pm UTC

Reviewer: Sal from Houston, USA

Recently we hit ORA-600 ([2252]. Oracle support wants us to give current timestamp on all our remote machines/databases where we connect using dblinks. One choice is to ask each DBA of the remote system to run select and the date command on their own machine/databases.. but .. is there a way that I can use these dblinks in my database and run a command from sqlplus prompt which will give me the database timestamp as well as the host timestamp on all remote databases/machines?

Thanks!

database link in between schemas of same database

July 21, 2011 - 3:59 am UTC

Reviewer: A reader

Dear Tom,

I hope you are doing well. In my production database I found that DB links are defined between two schemas. I heard that Oracle do not recommend us to create a database link between schemas in the single database. Now I am trying to find a way to convince my client so that we can convert those areas where db links are being used into views/synonyms.
I tried to fetch any table data through database link and without database link. But in that way I didn't find any notable change:
SQL> set autotrace on
SQL> alter system flush shared_pool;

System altered.

SQL> select count(*) from hisprod.ST_BATCHWISE_ITEM_DTL;

  COUNT(*)
----------
      5825


Execution Plan
----------------------------------------------------------
Plan hash value: 1334800570

-------------------------------------------------------------------------
| Id  | Operation             | Name    | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |         |     1 |     8   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE       |         |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| IND_SBI |  5785 |     8   (0)| 00:00:01 |
-------------------------------------------------------------------------


Statistics
----------------------------------------------------------
       1392  recursive calls
          0  db block gets
        375  consistent gets
          0  physical reads
          0  redo size
        412  bytes sent via SQL*Net to client
        400  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
         52  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> alter system flush shared_pool;

System altered.

SQL> select count(*) from ST_BATCHWISE_ITEM_DTL@CIS_HMS;

  COUNT(*)
----------
      5825


Execution Plan
----------------------------------------------------------
Plan hash value: 1334800570

-----------------------------------------------------------------------------------
| Id  | Operation              | Name    | Rows  | Cost (%CPU)| Time     | Inst   |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT REMOTE|         |     1 |     8   (0)| 00:00:01 |        |
|   1 |  SORT AGGREGATE        |         |     1 |            |          |        |
|   2 |   INDEX FAST FULL SCAN | IND_SBI |  5785 |     8   (0)| 00:00:01 | TMCPR~ |
-----------------------------------------------------------------------------------

Note
-----
   - fully remote statement


Statistics
----------------------------------------------------------
        402  recursive calls
          0  db block gets
         64  consistent gets
          0  physical reads
          0  redo size
        412  bytes sent via SQL*Net to client
        400  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          5  sorts (memory)
          0  sorts (disk)
          1  rows processed


Kindly help me how I can prove it to my client the performance degradation issue while using DBlinks in same database?
Tom Kyte

Followup  

July 22, 2011 - 1:51 pm UTC

use sql_trace and tkprof. time something that actually does something measurable. Like select * from t@remote. the overhead of returning a single insignificant count(*) over the link won't be large. Returning sets of data would be.

Point out these things:

a) all modifications will be a two phase commit, that is expensive.

b) any reference to another schema's objects will create a new session in the database - meaning you need to support two times as many sessions as you should be.

c) the initial touching of the other schema in a session will require a long wait - to start up the database connection

d) you are transferring all of the data over the network.

e) distributed query optimization of complex multi-table queries is not nearly as good as a single local query would be.

f) Tom says this is the silliest thing he has seen in a long time and can see no defense for doing it. (I had to throw that in there, I cannot imagine the thought process, the logic - that a person used to think this is a "good idea")

database link in between schemas of same database

July 27, 2011 - 5:51 am UTC

Reviewer: A reader

Dear Tom,

Thanks for this reply. I am more concern about this types of database links which will be implemented in standby databases. There is plan to implement the data guard (using phsycial standby database). But I am afraid that since database link uses TNS entry and physical standby would be using a separate TNS entry from primary, this might be a risk of transaction failing. Isn't it?
Tom Kyte

Followup  

July 28, 2011 - 6:59 pm UTC

no, we don't care about database links during redo apply, we are just applying redo - we don't actually reach out and touch the remote databases on the standby when it is in managed recovery mode, we are just applying the redo stream.

it wouldn't make sense to touch the remote database on the standby - they would have different data during the replay of the transaction (it is at a later date) than they did when the transaction first happened.

it is still the *sillest* thing, and I am using the word silly as a euphanism for another word that starts with S.

database link in between schemas of same database

July 29, 2011 - 1:56 am UTC

Reviewer: A reader

Dear Tom,

Yes, even I am eager to change the codes where it is using dblink. I want to take your opinion on how it can be done;
There are many trigger set in the application level which are accessing both schemas whenever any insertion, deletion, update is taking place. And this is happening in huge number of tables in both the schemas in the database.
Therefore should I have to use that much Synonyms (for insert/update/delete) or view (for select) for those tables being accessed in both the schema?
[Please note: I want to avoid prefixing the tables like <otherschema>.<table_name> inside the codes]
Tom Kyte

Followup  

August 01, 2011 - 11:28 am UTC

[Please note: I want to avoid prefixing the tables like <otherschema>.<table_name> inside the codes]


why, that would be my first choice by far.

with private synonyms being a second choice.

with views being a third choice

and public synonyms NOT being a choice at all.

database link in between schemas of same database

August 01, 2011 - 1:19 pm UTC

Reviewer: A reader

Dear Tom,

Thanks for you views. But using a single dblink on remote schema level I can get access of any object within that remote schema. Therefore could there be any such other object (like a type of synonym,etc) which I can create for a remote schema level and I can define any object within that remote schema through that object?
You can simply understand that I want to avoid those individual identification of remote schema objects through specifying so many views/synonyms ,etc
Tom Kyte

Followup  

August 01, 2011 - 2:12 pm UTC

You can simply understand that I want to avoid those individual identification of remote schema objects through specifying so many views/synonyms ,etc


not really, I don't have any problem with being EXPLICIT. You are already being explicit right now.

You are querying "select * from t@some_schema"

Now you will query "select * from some_schema.t"


what is the big deal? It is basically the same only much faster and less resource intensive

database link in between schemas of same database

August 01, 2011 - 9:51 pm UTC

Reviewer: A reader

Dear Tom,

Thanks for the clarification. But we have a development database as well where schema names are bit different (like "devchema" of development for "prodschema" of production). Therefore if I define 'hard coded' schema names inside the code like "<prodschema>.<tablename>" in production database, then the schema name has to be changed in so many codes (like "<devchema>.<tablename>") when the codes have to be tested in the development database.
Therefore do you suggest that I have to rename the development schema as same as production for that? or there is any other way out here?
Tom Kyte

Followup  

August 02, 2011 - 7:05 am UTC

why would you do that? To have different schema names?? To make testing harder I assume?

Therefore do you suggest that I have to rename the development schema as same as production for that? or there is any other way out here?


yes, that would be something that would make sense. short of that you are looking at views or private synonyms.

database link in between schemas of same database

August 05, 2011 - 9:24 am UTC

Reviewer: A reader

Dear Tom,

Thanks for the answer. My development team will be replacing those dblinks within same database by synonyms/views. But this will take some time further.
But, Now a days we are almost hitting with TNS-12520 or some other TNS error. Also I am observing that there are too many INACTIVE sessions in the database.
1) Can setting idle_time for 30 mins in the profile of the specific users minimize the INACTIVE sessions issue?
2) What do you suggest better?

Please help me until we convert the changes in the codes.
Tom Kyte

Followup  

August 05, 2011 - 1:21 pm UTC

1) the sessions will just be 'sniped', they will still exist until the client disconnects or you physically disconnect them.

What *causes* the too many idle sessions - instead of trying to work around something - why not fix it?

2) fix the root cause? Lower the size of connection pools for example.

database link in between schemas of same database

August 06, 2011 - 3:12 am UTC

Reviewer: A reader

Dear Tom,

Thanks for the response.
1)One question- Does exiting the parent session exits the child sessions (connecting internally through DBlink in same database) as well? If not then I think that our .NET application is not properly exiting from the parent session though there is connection close command. That is why there might be INACTIVE sessions. what is your comment on these?
2) You alos said "Lower the size of connection pools for example"....well how to do that? can you please explain a bit?

database link in between schemas of same database

August 06, 2011 - 3:12 am UTC

Reviewer: A reader

Dear Tom,

Thanks for the response.
1)One question- Does exiting the parent session exits the child sessions (connecting internally through DBlink in same database) as well? If not then I think that our .NET application is not properly exiting from the parent session though there is connection close command. That is why there might be INACTIVE sessions. what is your comment on these?
2) You alos said "Lower the size of connection pools for example"....well how to do that? can you please explain a bit?
Tom Kyte

Followup  

August 06, 2011 - 8:38 am UTC


1) I'm not sure what you mean by parent/child.

If you mean "parent = my session, child = session created by opening a database link in that session", then yes - if you log off of the parent, the 'chilren' will close.

2) go to your middleware and configure it, you configure connection pools there and "how" depends entirely on the infrastructure you are using.

dblink and tnsnames.ora

September 08, 2011 - 5:56 am UTC

Reviewer: RobK from Budapest

Hi Tom!

I have a running (10.2) database instance to which I can connect as dba. It's on Windows.

I created I dblink which is supposed to use tnsnames.ora config file:

create database link rlink connect to x identified by x using 'HUBX';

I don't know from which directory the oracle service was started. I don't know the OS global variable settings. I can't read the registry.
Hence I can only guess the location of tnsnames.ora file being used by the database.

Is there any way to avoid the guesswork and retrieve the path of the tnsnames.ora being used from the database?

Thanks in advance.
Rob

Tom Kyte

Followup  

September 08, 2011 - 5:36 pm UTC

if you don't know any of that, you don't have the ability to log onto the database server, and even if you do, you shouldn't be able to read any of the files you'd be looking for - so why do you care? You aren't the DBA of that database - you cannot see the file even if you knew where it was????

You'd have to know the environment of the server - and you shouldn't be guessing, you'd be ASKING the people that know and have access to the file - the DBA's

In short, no - not really - you'd have to have at least a tiny bit of information to figure out the rest.

dblink and tnsnames.ora

September 09, 2011 - 4:19 am UTC

Reviewer: A reader

Thanks for the reply!

Let me ask a slightly different question.
You are requested to debug a dblink network problem. The windows server -where the dblink is present- has 3 different tnsnames.ora files. One in %ORACLE_HOME%\network\admin, one under %TNS_ADMIN% defined by user environment, and the last one under %ORACLE_HOME%\database.

Note that the registry where %ORACLE_HOME%\bin\oracle.key points contained no TNS_ADMIN setting.

After renaming 2 to tnsnames.off and having one tnsnames.ora it turned out that %ORACLE_HOME%\database was the path being used.

To my best knowledge this is the search order for the tnsnames.ora file.

1. Oracle Net files in present working directory (PWD/CWD)
2. TNS_ADMIN set for each session by a user-defined script
3. TNS_ADMIN set as a global environment variable
4. TNS_ADMIN as defined in the registry
5. Oracle Net files in %ORACLE_HOME%/network/admin (Oracle default location)

And here are the questions that came to me when i was trying to understand how oracle decided it was using %ORACLE_HOME%\database:


1) Is the above list correct? More specifically is the order used by the oracle server (e.g the db link)? I cannot exclude that oracle server uses slightly different list compared to a sqlplus session.

2) If this is the correct list for oracle server then what does "1. present working directory" mean? How do I know how the current working directory defined for the service? If I don't know this it makes little use looking at the remaining points.

3) How can I check "2. TNS_ADMIN set for each session by a user-defined script"

4)
So the whole point is really that I would need a receipt for finding out
a) which location is used
b) currently which of the 5 possible definitions is in effect

5) Do you think this feature makes sense?
If currently we cannot get this information from the database, then I would see this as a useful feature:

select * from v$tns_admin;
LOCATION METHOD
------------------ -------------------
c:\vau REGISTRY

select * from v$tns_admin;
LOCATION METHOD
------------------ -------------------
c:\db1home\network\admin DEFAULT

Thanks for listening.
Rob.
Tom Kyte

Followup  

September 09, 2011 - 7:25 am UTC

1,2) the tnsnames.ora is found based on the database environment for dblinks, NEVER on the user/session environment

we don't look in the current working directory, not for dblinks - it is all based on the database server instance, not the user session.

we use tns_admin if set, and that would be for the oracle database account that is used to start the database - nothing to do with the user session

then it should be oracle_home\network\admin

3) does not come into play
4) user sessions do not count
5) again, the DBA that services this database should have been able to rattle off the location of the sole tnsnames.ora file for the server, they have been managing it after all.

dblink and tnsnames.ora

September 09, 2011 - 4:19 pm UTC

Reviewer: A reader

Thanks Tom!

In this case we just couldn't rely on the dba, because he messed everything up, and this was just his first effort to set up a test standby environment.

I posted my questions here for understanding the underlying mechanisms and rules for dblinks (which I think are not well documented)

I also was looking for the quickest way of debugging such issues. that's why I was looking for a "v$tns_admin" select.

Thanks again,
Rob.

September 20, 2011 - 5:48 am UTC

Reviewer: ms from India

If two sessions are accessing the same (working) db link and one of the sessions drops and recreates the link (same name) with a wrong password say and makes it non-working, why is it that the other session is still able to access the data via the link as though the link remains unchanged and functional?

Tom Kyte

Followup  

September 20, 2011 - 6:41 pm UTC

because the link is already opened - it is connected - we only need the link information when we first establish the connection

September 20, 2011 - 10:08 pm UTC

Reviewer: A reader

So is it that the connection to link association is made when the session uses the link for the first time and any changes to the link, including a drop and recreate, are not reflected in the resetting the connection?

Thanks for your time Tom!

procedural call over db link

October 04, 2011 - 6:41 am UTC

Reviewer: A Reader

Hello Tom,

Thanks for your time.

we raised the issue (03113 ) with Oracle support.

Need some clarification...( How?)

Database A : 9.2.0.8 has procedure p_A
Database B : 10.2.0.3 has procedure p_B


- database A has procedure p_A which in turns calls the procedure p_B inside it using db link.
(we DO DML on the remote tables using p_B )
- procedure p_B has COMMIT at the end in it.

When we execute the remote procedure using

SQLPLUS> exec p_A(arg1, arg2);

It get executed successfully. However

When we call p_A through application using JAVA file

we are seeing the execution failing intermittently with the following error.

ORA-02068: following severe error from DBLINK.WORLD
ORA-03113: end-of-file on communication channel
ORA-02068: following severe error from DBLINK.WORLD
ORA-03113: end-of-file on communication channel
ORA-06512: at "OWNER.package_name", line 309
ORA-06512: at line 1
. SQL Stmt : BEGIN package_name.p_A(arg1,arg2); END;


We did direct call using SQL*PlUS sevral time it all succeeded but failed often using Application.

fix applied was

- Invoke below immediately after remote procedure call ( p_B)

DBMS_SESSION.CLOSE_DATABASE_LINK ('DBLINK.WORLD');

This resolved the issue.


Question/s

a) How closing database link helped here?
Tom Kyte

Followup  

October 04, 2011 - 11:34 am UTC

please utilize support for this - It is nothing I can reproduce so I don't have any information about it personally.

procedural call over db link

October 04, 2011 - 6:42 am UTC

Reviewer: A Reader

Hello Tom,

Thanks for your time.

we raised the issue (03113 ) with Oracle support.

Need some clarification...( How?)

Database A : 9.2.0.8 has procedure p_A
Database B : 10.2.0.3 has procedure p_B


- database A has procedure p_A which in turns calls the procedure p_B inside it using db link.
(we DO DML on the remote tables using p_B )
- procedure p_B has COMMIT at the end in it.

When we execute the remote procedure using

SQLPLUS> exec p_A(arg1, arg2);

It get executed successfully. However

When we call p_A through application using JAVA file

we are seeing the execution failing intermittently with the following error.

ORA-02068: following severe error from DBLINK.WORLD
ORA-03113: end-of-file on communication channel
ORA-02068: following severe error from DBLINK.WORLD
ORA-03113: end-of-file on communication channel
ORA-06512: at "OWNER.package_name", line 309
ORA-06512: at line 1
. SQL Stmt : BEGIN package_name.p_A(arg1,arg2); END;


We did direct call using SQL*PlUS sevral time it all succeeded but failed often using Application.

fix applied was

- Invoke below immediately after remote procedure call ( p_B)

DBMS_SESSION.CLOSE_DATABASE_LINK ('DBLINK.WORLD');

This resolved the issue.


Question/s

a) How closing database link helped here?

..procedural call over db link

October 05, 2011 - 2:25 am UTC

Reviewer: A Reader

Thanks Tom and sorry about the repeat of the review above.

regards

Data Moving over dblink

October 22, 2011 - 4:59 am UTC

Reviewer: A reader

Moving data by using dblink there are 72K records but it taking very much time. I separate session if see the sequence value (being used in this insertion), it is not increasing. What is happening? Although performed this activity with large number of volume and in less time. What areas need to be seen?
Tom Kyte

Followup  

October 22, 2011 - 8:01 pm UTC

72,000 records is teeny tiny and will not take long over any 'realistic' network.

If you don't see the sequence increasing, it is NOT the movement of data - rather it is the processing of the query in the first place. Your query to get 72,000 records seems to be the bottleneck.

If you just RUN the query - how long does it take (no inserts, no sequences, just fetch the data)

Merge join Cartesian (DB Link)

November 04, 2011 - 5:48 am UTC

Reviewer: Prashant from Mumbai, India

Hi Tom

I have 3 tables in site and 1 in remote. The query started doing a merge join cartesian. This always puts me off seeing a MJC (I know when MJC can be used) but why does it do an MJC in this case? I wanted to run a trace but this query doesn't complete so I am not sure how to do it.

I have stats correctly maintained as you can see in the dbms_xplan results below. The query eventually fails after exhausting temp space (160 GB). Then I introduce a ROWNUM = 1 in the EXISTS clause and the explan changes for the better (I thought EXISTS works as ROWUM=1 isn't). Now the
results are returned in 10 mins because it selects a much better execution path.

SELECT <list of columns> FROM
T_LINES_ALL A,
T_HEADERS_ALL B,
T_EVENTS_ALL C
WHERE
A.AE_HEADER_ID =B.AE_HEADER_ID
AND B.ACCOUNTING_EVENT_ID=C.ACCOUNTING_EVENT_ID
AND EXISTS
(
SELECT
TGT.AE_LINE_ID
FROM
T_EVENT_DL TGT
WHERE
TGT.AE_LINE_ID =A.AE_LINE_ID
AND TGT.PERIOD_NAME=B.PERIOD_NAME
);

------------------------------------------------------------------------------------------------
|Id|Operation |Name |Rows |Bytes|TempSpc|Cost (%CPU)|Time |Inst |IN-OUT|
------------------------------------------------------------------------------------------------
| 0|SELECT STATEMENT | | 1| 368 | | 195K (1)|00:58:43| | |
|*1| HASH JOIN | | 1| 368 | | 195K (1)|00:58:43| | |
| 2| MERGE JOIN CARTESIAN| | 1| 336 | | 195K (1)|00:58:42| | |
|*3| HASH JOIN | | 1| 320 | 48M| 195K (1)|00:58:40| | |
| 4| TABLE ACCESS FULL |T_LINES_ALL | 165K| 46M| | 1027 (1)|00:00:19| | |
| 5| SORT UNIQUE | | 123M|2592M| |57792 (1)|00:17:21| | |
| 6| REMOTE |T_EVENT | 123M|2592M| |57792 (1)|00:17:21|DL_ST~| R->S |
| 7| BUFFER SORT | |25662| 400K| | 137K (1)|00:41:21| | |
| 8| TABLE ACCESS FULL |T_EVENTS_ALL |25662| 400K| | 85 (0)|00:00:02| | |
| 9| TABLE ACCESS FULL |T_HEADERS_ALL|22906| 715K| | 85 (0)|00:00:02| | |
------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
1 - access("A"."AE_HEADER_ID"="B"."AE_HEADER_ID" AND "B"."ACCOUNTING_EVENT_ID"="C"."ACCOUNTING_EVENT_ID" AND
"TGT"."PERIOD_NAME"="B"."PERIOD_NAME")
3 - access("TGT"."AE_LINE_ID"="A"."AE_LINE_ID")

Remote SQL Information (identified by operation id):
----------------------------------------------------

6 - SELECT "AE_LINE_ID","PERIOD_NAME" FROM "EDWBAS"."AP_EVENT" "TGT" (accessing
'DL_STG_TO_EDW.COM' )

(2) Changed Exists Query with ROWNUM =1
SELECT <list of columns> FROM
T_LINES_ALL A,
T_HEADERS_ALL B,
T_EVENTS_ALL C
WHERE
A.AE_HEADER_ID =B.AE_HEADER_ID
AND B.ACCOUNTING_EVENT_ID=C.ACCOUNTING_EVENT_ID
AND EXISTS
(
SELECT
TGT.AE_LINE_ID
FROM
T_EVENT_DL TGT
WHERE
TGT.AE_LINE_ID =A.AE_LINE_ID
AND TGT.PERIOD_NAME=B.PERIOD_NAME
AND ROWNUM = 1
);

----------------------------------------------------------------------------------------
|Id|Operation |Name |Rows |Bytes|Cost (%CPU)|Time |Inst |IN-OUT|
----------------------------------------------------------------------------------------
| 0|SELECT STATEMENT | | 1 | 346| 488K (1)|02:26:25| | |
|*1| FILTER | | | | | | | |
|*2| HASH JOIN | | 166K| 54M| 1199 (1)|00:00:22| | |
|*3| HASH JOIN | |22976 |1077K| 171 (1)|00:00:04| | |
| 4| TABLE ACCESS FULL|T_EVENTS_ALL |25662 | 400K| 85 (0)|00:00:02| | |
| 5| TABLE ACCESS FULL|T_HEADERS_ALL|22906 | 715K| 85 (0)|00:00:02| | |
| 6| TABLE ACCESS FULL |T_LINES_ALL | 165K| 46M| 1027 (1)|00:00:19| | |
|*7| COUNT STOPKEY | | | | | | | |
| 8| REMOTE |T_EVENT | 1 | 22 | 3 (0)|00:00:01|DL_ST~| R->S |
----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

1 - filter( EXISTS (SELECT 0 FROM "TGT" WHERE ROWNUM=1 AND "TGT"."AE_LINE_ID"=:B1 AND
"TGT"."PERIOD_NAME"=:B2))
2 - access("A"."AE_HEADER_ID"="B"."AE_HEADER_ID")
3 - access("B"."ACCOUNTING_EVENT_ID"="C"."ACCOUNTING_EVENT_ID")
7 - filter(ROWNUM=1)

Remote SQL Information (identified by operation id):
----------------------------------------------------

8 - SELECT "AE_LINE_ID","PERIOD_NAME" FROM "EDWBAS"."AP_EVENT" "TGT" WHERE "AE_LINE_ID"=:1 AND
"PERIOD_NAME"=:2 (accessing 'DL_STG_TO_EDW.COM' )
Tom Kyte

Followup  

November 07, 2011 - 9:49 am UTC

it is doing the MJC because of this:

|*3|   HASH JOIN          |             |    1| 320 |    48M|  195K  (1)|00:58:40|      |      |



it is estimating a single row from that HASH join.

Additional information to above question

November 05, 2011 - 12:09 am UTC

Reviewer: Prashant from Mumbai, India

Database: Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production

Remote predicate above has correction to table name (since I changed table names to hide business names).

Query 1:
Remote SQL Information (identified by operation id):
----------------------------------------------------

6 - SELECT "AE_LINE_ID","PERIOD_NAME" FROM "EDW"."T_EVENT" "TGT" (accessing 'DL_STG_TO_EDW.COM' )

Query 2:
Remote SQL Information (identified by operation id):
----------------------------------------------------

8 - SELECT "AE_LINE_ID","PERIOD_NAME" FROM "EDW"."T_EVENT" "TGT" WHERE "AE_LINE_ID"=:1 AND
"PERIOD_NAME"=:2 (accessing 'DL_STG_TO_EDW.COM' )

Thanks but why does it estimate 1 row?

November 08, 2011 - 10:08 am UTC

Reviewer: Prashant from Mumbai, India

<<
it is doing the MJC because of this:

|*3| HASH JOIN | | 1| 320 | 48M| 195K (1)|00:58:40| | |




it is estimating a single row from that HASH join.
>>

Tom, Thank you so much for your reply. Yes you are right it estimates single row and hence does MJC. I feel stupid at having overlooked this. But can you please shed some light as to why do you think it estimates 1 row when the stats are correctly maintained?


Tom Kyte

Followup  

November 08, 2011 - 10:52 am UTC

It converted the where exists:

SELECT <list of columns> FROM
  T_LINES_ALL A,
  T_HEADERS_ALL B,
  T_EVENTS_ALL C
WHERE
  A.AE_HEADER_ID         =B.AE_HEADER_ID
AND B.ACCOUNTING_EVENT_ID=C.ACCOUNTING_EVENT_ID
AND EXISTS
  (
    SELECT
      TGT.AE_LINE_ID
    FROM
      T_EVENT_DL TGT
    WHERE
      TGT.AE_LINE_ID   =A.AE_LINE_ID
    AND TGT.PERIOD_NAME=B.PERIOD_NAME
  );




It estimated one row in both cases - just the ordering of the tables being processed was influenced by your use of rownum.

In both cases when it puts the remote together with the local data - it is estimating one row.

Distributed queries are particularly hard to optimize - the two databases do not share 100% of everything unfortunately. and when we get the wrong estimated cardinality - we often get the wrong plan (sometimes we get lucky and get the right plan in spite of ourselves)


how many rows does this query ultimately return?

Great insight

November 08, 2011 - 12:06 pm UTC

Reviewer: Prashant from Mumbai, India

Thanks Tom. The query returns around 110,000 rows.

Your point about "particularly hard to optimize distributed queries because Oracle doesn't know everything" is interesting.

Just to give a scenario of our current process and I have been advocating something similar but without knowledge of the above point that you have made.

We have a source system Oracle Apps from which we are pulling incremental data daily into a staging database and then running the above logic to identify records for update and another query using not exists for insert logic.


Source -> Staging (Truncate and Pull Incremental Data daily into the 3 tables (T_LINES_ALL,T_HEADERS_ALL,T_EVENTS_ALL) and then run the above logic to populate target table in this case T_EVENT@target db) -> Target

I have recommended that the above approach is inefficient and the following is recommended

(1) If we are using a separate database only for staging incremental data then we would be better off pulling the incremental data directly from source to target and hosts these tables in target and run the above logic in the target db

I have suggested to eliminate stage entirely and use the below approach to eliminate DB link for processing

Source -> Target (Truncate and Pull Incremental Data daily for the 3 source tables and then run the above logic to populate target table T_EVENT without having to use distributed query)

(2) For UPSERT logic we should use MERGE. Although I haven't tested it myself but I have read on your forums and elsewhere that is bench marked to be faster that UPDATE and INSERT

Can you please let me know if this is ok?

Thanks
Prashant
Tom Kyte

Followup  

November 08, 2011 - 12:57 pm UTC

(1) I agree, if I don't need to do distributed (and you hardly ever, rarely ever do) - I do not do it.

If there is an easy way to cut out the middle man - you'll benefit from it.


(2) in general, it would perform better than
a) update all rows that exist
b) insert the minus of src and tgt to get new.

Database link from 10g to 11g database

November 09, 2011 - 9:03 am UTC

Reviewer: A reader

Hi Tom - We recently upgraded a bunch of our application databases from Oracle 10g (10.2.0.4) to Oracle 11g (11.2.0.2) except for one database which is still in 10.2.0.4. There is a database link from this 10g database to one of the upgraded 11g databases. When both of the databases were in 10g, one particular report was taking 20 mins but since the upgrade the report is taking about 12 hrs. The only variable is that the database link now points from 10g to 11g. We did a complete schema statistics in 11g after the upgrade. Should we have done something with the dictionary stats and do you think that might contribute to a delay like this ? Any help is appreciated.

Thanks.
Tom Kyte

Followup  

November 09, 2011 - 11:27 am UTC

sounds like a plan change.

do you have your ASH/AWR/Statspack information from before the upgrade took place?

November 09, 2011 - 12:57 pm UTC

Reviewer: A reader

Is there a way we can get historical execution plans ?
Tom Kyte

Followup  

November 09, 2011 - 1:43 pm UTC

yes:

ASH/AWR/Statspack


do you have any of that from before.

if not, no.

November 09, 2011 - 2:05 pm UTC

Reviewer: A reader

I went through Advisor Central -> ADDM and I can see the SQL from the date that I am interested in but when I click to see the plan I get a message "Execution plan is not available", and I also tried to see the snapshots and I dont see the snapshots from the timeframe I am interested in. So I dont think I can get it.
Tom Kyte

Followup  

November 09, 2011 - 2:18 pm UTC

Well, I believe it to be a plan change most likely - so your approach would be "query tuning" - trying to affect the plan in a positive fashion. Unfortunately - since you don't keep a long history (probably just have the default of a week - which I think is about 35 days too short), we don't know what plan we are targeting (or even if it was a plan change).


Unless you can test in your test environment against the old setup that is.

DB Links

December 08, 2011 - 3:12 pm UTC

Reviewer: HARIHARAN from INDIA

Thanks TOM..
We have a table in one schema. Eg: Schema A containing table test. created synonym test (same name) in B schema using DB links.
Every day in A Schema adding/removing records in the objects like tables.
Please clarify whether data is automatically refreshed in our created synonyms (B Schema)or we need to schedule jobs.

Also, please clarify which one is better (View/Synonym) for the above cases. Some times we use above objects in stored procedure also.
Tom Kyte

Followup  

December 09, 2011 - 4:03 pm UTC

synonyms are just pointers, the point to the real data, they are not copies, just a nickname.


My name is Thomas, but you can call me by my synonym Tom. They are the same thing.


I prefer to use views over db links. Views import the metadata from the remote site into your local dictionary, synonyms would not. that means you can query user_views to see the columns/types of the remote table - but if it were a synonym - you would have to do a remote query to do the same. Makes compiling code locally faster too - you don't have to do a remote query to compile procedures and so on.

To Steve

March 05, 2012 - 4:02 pm UTC

Reviewer: Alexander

This is a long shot but if you get lucky and can change the sdk_user user's pw on your database to be what it is in the remote (probably just throw the same error) then log in as sdk_user and omit the user/name password clause on the create link and let it implicitly use the user/pw you are logged in as.
Tom Kyte

Followup  

March 06, 2012 - 6:52 am UTC

Actually, I'm going to remove the comment above and post it here again - I just realized they might have posted their actual password...



...
We're trying to connect to a sql server database but the password is too long. For example:
SQL> create database link net2 connect to "sdk_user" identified by "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" using 'net2a';
create database link net2 connect to "someuser" identified by "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" using 'net2a'
*
ERROR at line 1:
ORA-00972: identifier is too long

We cannot change the sqlserver password - it's not our system, nor are the 3rd party prepared to
create a new read only password. Is there a solution on the Oracle side?




Alexander - that won't work, the maximum password length is 30

March 06, 2012 - 1:13 pm UTC

Reviewer: Alexander

Yes I realized after hitting submit I could easily test by trying to create a user with that password. No dice.

connect sql server 2008 from oracle 11g

September 12, 2012 - 3:34 am UTC

Reviewer: subhan from Pakistan

i want to connect sql server database from oracle 11g.

oracle 11(g)
-64 bit
-linux (oel) 64bit

Sql serevr 2008
-windows server 2003
-64 bit
these on the same network.please help me how to connect it

getting ORA-12154: TNS:could not resolve service name error when creating a database link

September 25, 2012 - 6:11 am UTC

Reviewer: Nilesh Kumar from Kolkata, India

Hi Tom,
i have TNS.ORA file at my clint PC with following desc
dbname =
DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = HOST-IP)(PORT = HOST-PORT))
(CONNECT_DATA= (SERVER=DEDICATED)(SERVICE_NAME = DB_SID) ))

and with this connect string i am able to log on to this remote DB by giving database as dbname (means their is an entry of DB_SID in tns file at server), but when creating a db link with this same description with following syntax

create database link dblink1 connect to USER identified by PASSWORD using 'dbname';
or
create database link dblink1 connect to USER identified by PASSWORD using 'DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = HOST-IP)(PORT = HOST-PORT))
(CONNECT_DATA= (SERVER=DEDICATED)(SERVICE_NAME = DB_SID) ))';

with this link, i am not able to query any table or view and am getting message "ORA-12154: TNS:could not resolve service name".

so please tell
1. what is the probable cause of error
2. is it possible to block user coming to my database with this kind of DB Link based on userid or the network address they are coming from.
Tom Kyte

Followup  

September 27, 2012 - 8:21 am UTC

1) the database cannot, should not, see your tnsnames.ora file, it can only see its tnsnames.ora. you'd need this entry on the server

2) you can use the listener.ora to provide a white/black list of hosts, yes. you can block by IP address.

http://docs.oracle.com/cd/E11882_01/server.112/e10575/tdpsg_network_secure.htm#sthref320


Different explain plan for remote query depending on where I run it?

September 26, 2012 - 11:30 am UTC

Reviewer: Robert from Memphis, USA

Hi Tom,

Oracle versions 11.2.0, 10.2.0

I have a query against V$RMAN_STATUS which I am running from a central database and linking to several other databases. i.e.

select .... from v$rman_status@db1 .... ;
select .... from v$rman_status@db2 .... ;
select .... from v$rman_status@db3 .... ;
etc.

But there are odd things with the explain plans...

When I run this query linking to "db3" *from* db_x I get one plan (a good one)
.. but when I run this same query *from* db_y to "db3" (same TO database, "db_3") I get a different plan (a bad one).

The explain plan appears to be showing the plan of the remote database (db3), not the originating databases (db_x, db_y) (as I would expect).

Will you please help me understand how a different originating (FROM) database causes a different explain plan running the same query on same remote database?

Thank you,

Robert.
Tom Kyte

Followup  

September 27, 2012 - 8:34 am UTC

if your originating databases are different versions/patch levels, you have two different optimizers going, different optimizers =>different plans.

are the estimated cardinalities the same?

you might consider using the driving_site hint to have the query always optimized at the *source* database if that makes sense.

Not understanding....

September 27, 2012 - 11:17 am UTC

Reviewer: Robert from Memphis, USA.

Tom,

Thanks, I will try the driving site hint.
But as far as different versions having different optimizer settings.... totally understand... but it is a 'simple' single table query selecting from only one table on remote site.
Wouldn't all optimization occur on the remote site?
And the remote site is constant... only source site is different (?)
Can you please clarify?

Thanks,

Robert.
Tom Kyte

Followup  

September 27, 2012 - 3:21 pm UTC

tell me what is different about the plans then??? you had lots of .....'s in your example, it didn't look like a simple single table query to me.

Tried to paste.....

October 01, 2012 - 4:13 pm UTC

Reviewer: Robert from Memphis, USA.

Tom,

Thanks for your latest response.
I had tried to paste everything back several days ago, but it ran out of room in the text pane. I figured maybe you had a limit on response sizes but not on initial questions so I was going to wait until you had an open question I could ask.
Will get that info to you.

Thank you,

Robert.
Tom Kyte

Followup  

October 09, 2012 - 11:20 am UTC

the size issue of a review should be fixed, it was caused by an APEX upgrade.

this is a test

October 09, 2012 - 11:23 am UTC

Reviewer: A reader

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I opened a new question about this....

October 09, 2012 - 1:44 pm UTC

Reviewer: Robert Wood

Tom,

<< regarding my above post from several days ago >>

I was able to open new question about this yesterday.
This new question of mine should be framed more succinctly and to the point.
Also, I have captured all explain plan info for all 3 examples (but it must have been before the APEX issue was fixed)... so when you get to my new question I am ready to send the explain plan info if you should ask for additional info.

Thank you,

Robert.

i have trouble with 2068, 3113

February 14, 2013 - 1:32 am UTC

Reviewer: Sean from Australia

i was trying to make a db link from single server to RAC server and below is my history

testdevdb:[/oracle10g/app/oracle]sqlplus

SQL*Plus: Release 10.2.0.5.0 - Production on Thu Feb 14 16:08:38 2013

Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.

Enter user-name: /as sysdba   

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Data Mining and Real Application Testing options

SQL> 
SQL> create database link ln_sys_to_testdb
  2  connect to TESTos
  3  identified by opentest
  4  using 'TESTDB';

Database link created.

SQL> select * from dual@ln_sys_to_testdb;
select * from dual@ln_sys_to_testdb
                   *
ERROR at line 1:
ORA-02068: following severe error from LN_SYS_TO_KLAODB
ORA-03113: end-of-file on communication channel


SQL> create database link ln_sys_to_ip     
  2  connect to testos
  3  identified by opentest
  4  using '192.168.111.111:1521/TESTDB';

Database link created.

SQL> select * from dual@ln_sys_to_ip;
select * from dual@ln_sys_to_ip
                   *
ERROR at line 1:
ORA-02068: following severe error from LN_SYS_TO_IP
ORA-03113: end-of-file on communication channel


SQL> create database link ln_sys_to_wrongpass
  2  connect to testos
  3  identified by opentesta
  4  using 'TESTDB';  

Database link created.

SQL> select * from dual@ln_sys_wrong_pass;
select * from dual@ln_sys_wrong_pass
                   *
ERROR at line 1:
ORA-01017: invalid username/password; logon denied
ORA-02063: preceding line from LN_SYS_WRONG_PASS


SQL> um....... what the hell........ destination knows which one is correct login... but.. no db link...
SP2-0734: unknown command beginning "um....... ..." - rest of line ignored.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Data Mining and Real Application Testing options

lets try to connect using SQLplus with testdb alias..

testevdb:[/oracle10g/app/oracle]sqlplus klaoos/openklao@testdb

SQL*Plus: Release 10.2.0.5.0 - Production on Thu Feb 14 16:18:13 2013

Copyright (c) 1982, 2010, Oracle.  All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, Data Mining and Real Application Testing options

SQL> What??????????????? it works.....
SP2-0042: unknown command "What?....." - rest of line ignored.
SQL> exit
Disconnected from Oracle Database 10g Enterprise Edition Release 10.2.0.5.0 - 64bit Production
With the Partitioning, Real Application Clusters, Data Mining and Real Application Testing options
testdevdb:[/oracle10g/app/oracle]

both source and destination has same version of oracle
source is single server and the destination is 2 node RAC

1. remote access using SQLPLUS with TESTDB alias works fine

2. 3rd db link has wrong password and the destination answered that the password is wrong.. so network is fine

any suggestion to me?

Tom Kyte

Followup  

February 14, 2013 - 7:32 am UTC

stop right there:

Enter user-name: /as sysdba



DO NOT DO THAT, do use use sysdba for 'regular stuff'. Only use sysdba when there is *no other alternative*. period. do not use sys, sysdba, sysoper, system - just don't. use your OWN account.

.... um....... what the hell... ...

indeed, why would you put that here? what's up with that. If you want to ask a technical question - fine, go for it.

If you totally want to turn me off - curse, use IM speak, whatever.




please utilize support for an ora-3113, ora-7445, ora-600. Something is obviously happening after the authentication on the remote server that is causing the process that connected to the database to fail. You might want to look at the logs on the remote server.


and don't forget - the tnsnames.ora you use could be and many times is *totally* different from the tnsnames.ora the server itself it using. You having shown that you are actually connecting to the same server - you'd have to use the ezconnect string to demonstrate that.

Parallel Insert through db link

May 29, 2013 - 6:07 am UTC

Reviewer: Raghav from India

Hi tom

Suppose, I have a table in local database and the same table is existing in remote database. Both tables are defined with parallel (degree default instances default) and the remote table is having 1.2 billion records.
I wish to pull (insert) data from remote database to local using db link. As per my understanding, the db link creates one thread and loads data in serial but not in parallel.

My question: Is there a way that we can pull the data in parallel using the db link? I.e., this session creating slave sessions (parallel threads) and pull the data in parallel.

Thanks & Regards
Raghav
Tom Kyte

Followup  

May 29, 2013 - 7:25 pm UTC

using datapump - yes.

using "do it yourself parallelism" - yes (or dbms_parallel_execute - search for either on this site)

but...

the best approach is going to be a transportable tablespace, don't unload and reload the table, just grab the datafiles - from a backup if you want. It'll move as fast as you can copy the files over.

How to Change the Value of INput parameter

May 30, 2013 - 12:32 pm UTC

Reviewer: Bharath from india

I have the procedure which 2 inputparamaters so the values that is going to pass as input parameter is 0 and 0 so i need to reolace the input paramaetre values with others in oracle
Tom Kyte

Followup  

May 30, 2013 - 2:55 pm UTC

huh???

just do it, I don't know what you mean or why this would be hard. Inputs are changeable.

you give no information here as to the problem you are actually encountering.

driving_site hint use in a query connecting to multiple databases

June 18, 2013 - 8:58 am UTC

Reviewer: Arun from India

we are using a query which uses a remote table and two other views populated from another remote DB. The query is giving 'ORA-02019: connection description for remote database not found' when driving_site hint is applied. without it query runs fine.

Select /*+ DRIVING_SITE(c) */
a.person
from table1@remote1,
table2,--view to remote database remote2
table3,--view to remote database remote2
table4--local table
where a.item1= b.item2
and b.item3 =c.item4
and c.item5 = d.item6
Tom Kyte

Followup  

June 18, 2013 - 4:02 pm UTC

please utilize support for that one - that would be a bug.

Dblink issue with Active data guard in 11g

August 20, 2013 - 9:06 pm UTC

Reviewer: Romit Acharya from Boston,MA USA

Hi Tom,

We have setup active data guard(ADG) on 11gR2 env. We have a 10gR2 reporting database (RC).

RC tries to fetch data from ADG env, over a db link. We face an intermittent issue.
Ths sql query( only select statements) which run from RC fails with below error message.

ORA-04052:error occured when looking up remote object
ORA-00604:error occured at recursive SQL level 1
ora-16000:database open for read-only access
ORA-02063:preceing 2 lines from DWFEEDD_PRDFIN

No trace or error file is generated. Please suggest as what can be the issue.

As said, it works mostly but fails in between.

Error calling user defined function

September 07, 2013 - 10:27 am UTC

Reviewer: Soumya from KOLKATA

/******************************************************\
[DATABASE : A] [HOST : GSL-KOL-DT-305] [SCHEMA : GLOB]
\******************************************************/
CREATE TABLE DBLINK_TEST_GLOB
(COL1 VARCHAR2(100));

/******************************************************\
[DATABASE : B] [HOST : LT-05-V2] [SCHEMA : GSL1]
\******************************************************/

DROP PUBLIC DATABASE LINK "GINESYS_GLOB";

CREATE PUBLIC DATABASE LINK "GINESYS_GLOB"
CONNECT TO GLOB
IDENTIFIED BY GMPL
USING '(DESCRIPTION =(ADDRESS = (PROTOCOL = TCP)(HOST = GSL-KOL-DT-305)(PORT = 1521))(CONNECT_DATA =(SERVER = DEDICATED)(SERVICE_NAME = GINESYS)))';

--=========================================
--STEP1 (SUCCESSFUL)
--=========================================

DELETE FROM DBLINK_TEST_GLOB@GINESYS_GLOB;

INSERT INTO DBLINK_TEST_GLOB@GINESYS_GLOB
SELECT USERNAME FROM DBA_USERS;

COMMIT;

SELECT * FROM DBLINK_TEST_GLOB@GINESYS_GLOB;

--=========================================
--STEP2 (FAILURE)
--=========================================

CREATE OR REPLACE FUNCTION DB_FUN_DBLINKTEST RETURN CHAR
IS
BEGIN
RETURN ('SOUMYA');
END;
/

DELETE FROM DBLINK_TEST_GLOB@GINESYS_GLOB;

COMMIT;

INSERT INTO DBLINK_TEST_GLOB@GINESYS_GLOB
SELECT SUBSTR(DB_FUN_DBLINKTEST(),1,50) FROM DUAL;

--ERROR : ORA-02069: global_names parameter must be set to TRUE for this operation

ALTER SYSTEM SET GLOBAL_NAMES = TRUE;

INSERT INTO DBLINK_TEST_GLOB@GINESYS_GLOB
SELECT DB_FUN_DBLINKTEST() FROM DUAL;

--ERROR : ORA-02085: database link GINESYS_GLOB.REGRESS.RDBMS.DEV.US.ORACLE.COM connects to GINESYS.REGRESS.RDBMS.DEV.US

Note : If any Select statement contains user defined Function then Insert statement failed to execute

Tom Kyte

Followup  

September 10, 2013 - 9:35 am UTC

that particular operation needs global names to be true, it says that pretty clearly:

$ oerr ora 2069
02069, 00000, "global_names parameter must be set to TRUE for this operation"
// *Cause: A remote mapping of the statement is required but cannot be achieved
//         because global_names should be set to TRUE for it to be achieved
// *Action: Issue alter session set global_names = true if possible



and when global names = true, your database naming and dblink naming must follow strict conventions put in place to make sure you are not accidentally connecting to the wrong database. Your dblink must be named after the remote databases global name.

so, if you want to do this, you need global naming (you should be using global naming regardless) and in order to use global naming you must name your database links after the global name of the database they connect to. this forces unique, known names for databases connected in a distributed fashion (and reduces the chance of doing something really bad in the wrong database)

dblink

September 20, 2013 - 5:11 am UTC

Reviewer: SOUMYA from KOLKATA, INDIA

Hi Tom,

as per your suggestion I already altered the system, then also its gives error.

My only question is why Statement 1 works but Statement 2 not.

Statement 1
============
INSERT INTO DBLINK_TEST_GLOB@GINESYS_GLOB
SELECT USERNAME FROM DBA_USERS;

Statement 2
============
INSERT INTO DBLINK_TEST_GLOB@GINESYS_GLOB
SELECT SUBSTR(DB_FUN_DBLINKTEST(),1,50) FROM DUAL;

Note : I used a function in select clause of Statement 2

Insert Data Through dblink

October 09, 2013 - 1:03 pm UTC

Reviewer: pawan from Karachi

Hello to All, I want to insert data through dblink to another remote database. My question is this archive of this inserting query are created in source or remote database ? synonyms of remote database are created in source database
Tom Kyte

Followup  

October 09, 2013 - 5:59 pm UTC

the redo and hence archives will necessarily be recorded on the database that actually does the insert.

so they would be generated on the remote database.

Size limit for data from remote database

October 14, 2013 - 6:43 pm UTC

Reviewer: MJ_Tech from Mumbai, INDIA

The whole thread was very helpful, but I wanted to know if there is some kind of limit to how much data can be accessed from remote database via database link.
I got the following error messages:
ORA-01652: unable to extend temp segment by 128 in tablespace TEMP
ORA-02063: preceding line from REM_DB_LINK
For one scenario I was expecting <1000 records from remote DB, and the query still failed.
So I was wondering what is the size limit, if any.
If not, then what might be the reason?
Tom Kyte

Followup  

November 01, 2013 - 6:22 pm UTC

there is no size limit.

you simply ran out of room in your temporary tablespace. that could happen for any query - a distributed one or a single database one.

it has nothing to do with database links.

more about 2 dblinks involved.

October 22, 2013 - 4:18 pm UTC

Reviewer: jimbo from Bolivia - South America

Hi
Sorry if I’m asking an already answered question, but here is the issue. We have 3 different databases, A, B and C. We have created an application that access and registers data in database C and reads data from A, B and C using something like this:

SELECT col1, col2 FROM tableX@A
WHERE condition01
UNION ALL
SELECT colX, colY FROM tableY@B
WHERE condition02;

And also like this:

SELECT table01.col10, table02.col20
FROM table01, table02@A
WHERE ….

All databases are running in same O.S. and also all of them are 11g (Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - 64bit Production).
We did this because databases A and B have tons of transactions and they have to be available 7 x 24 (telco’s business). Database C is used to register claims, tickets, etc. for clients residing in A and B.
My question is if you see any consideration that we should have or if this is a risky implementation.
Thank you very much, in advance, for your time.

Transfer from Local DB To Apps DB

December 26, 2013 - 7:31 am UTC

Reviewer: mohammad from Amman

Hi Tome ,,,

I like to transfer Data from Local DB in personal PC Scott \ tiger@orcl Table Name XX to Apps DB EBS
to the same table XX apps \ 123@prod , in the last month transfer data Automatically .

you can give me steps to do that..


thank you


Transfer Data from Local DB to Apps DB EBS --Backup

December 26, 2013 - 8:25 am UTC

Reviewer: Mohammad from Jordan

Hi Tome ,,,

When start up Application after shutdown Applications -- Backup --

i like to Copy Data from Local DB in personal PC Scott \ tiger@orcl Table Name = XX1 Append in Apps DB EBS
Table Name = XX2 in apps \ 123@prod


you can give me steps urgent urgent to do that..


thank you

Transfer Data from Local DB to Apps DB EBS --Backup

December 26, 2013 - 8:52 am UTC

Reviewer: Mohammad from Jordan

Hi Tome ,,,

When start up Application after shutdown Applications -- Backup --

I like to Copy Data automatically When start up Applications from Local DB in personal PC Scott \ tiger@orcl Table 1 scott user Name = XX1 Append in Apps DB EBS

Table 2 apps user Name = XX2 in apps \ 123@prod


You can give me steps by example urgent urgent to do this tasks ..


thank you

Db Link

January 15, 2014 - 9:01 am UTC

Reviewer: Meltem from Turkey

Hello Tom,
We have two databases A, B. A is production, B is archive. We copy data less specific dates to the B database using db links. I actually would like to make the B database tables read only to prevent access. Normally we cannot do this using dblinks because ddl's are forbidden. Do you know any other methods to make tables readonly which can be directly fired from the production db ? I would like to make the table read write, on the archive schedule, otherwise it should be read only...
Db version is oracle 11gR2

Thanks in advance
Tom Kyte

Followup  

January 15, 2014 - 8:21 pm UTC

as you noted you cannot do DDL over a dblink and to make them read only would require that.

you can use the database link to submit a job to dbms_job@remote_site. That job can do DDL (assuming the owner of the job has the direct ability to issue that DDL). the job will run shortly after you commit.


the other alternative is to host the code on b, let b pull the changes - instead of a pushing them.

ORA-04052 - Very Puzzled

June 18, 2014 - 9:08 am UTC

Reviewer: Al Ricafort from Hong Kong

Hi Tom,

I am issuing a very simple update statement in our production very much like this one:

update TABLEA set status = 'A', last_upd_date = sysdate, last_upd_by = 'ME' where key = 1234;


and I am getting this error:

ERROR at line 1:
ORA-04052: error occurred when looking up remote object
XXXXX.STATUS@AAAAA.WORLD
ORA-00604: error occurred at recursive SQL level 1
ORA-12535: TNS:operation timed out


I am puzzled because other than a trigger that will be fired which will insert a record into TABLEB, this table or TABLEB has no relationship whatsoever with the dblink XXXXX.STATUS@AAAAA.WORLD.

What is more puzzling is that if I do the update using the ROWID instead of the KEY no such error occurs.

Do you have any idea what is going on?

Thanks.

Question on DB Link

July 29, 2014 - 8:46 am UTC

Reviewer: Sandeep from Mumbai, India

On DB, we have observed SQLs which is without DBLINK name in it.

UPDATE "SAPSRP"."ZWMS_SKUMST_DB1" "A1" SET "TRN_ID" = :B2,"STATUS" = '5' WHERE "A1"."STATUS"='0' AND "A1"."WHSEID"=:B1 AND "A1"."CPUDT">'20130722' AND ROWNUM< (SELECT "A2"."CODE" FROM "CODELKUP"@! "A2" WHERE "A2"."LISTNAME"='DB_MAS_CNT')

UPDATE "SAPSRP"."ZWMS_DELTRN_DB1" "A1" SET "TRN_ID" = :B2,"STATUS" = '5' WHERE "A1"."STATUS"='0' AND "A1"."WMSID"=:B1 AND "A1"."VBELN"=ANY (SELECT "A2"."VBELN" FROM (SELECT DISTINCT "A4"."VBELN" "VBELN" FROM "SAPSRP"."ZWMS_DELTRN_DB1" "A4" WHERE "A4"."STATUS"='0' AND "A4"."WMSID"=:B1) "A2" WHERE ROWNUM< (SELECT "A3"."CODE" FROM "CODELKUP"@! "A3" WHERE "A3"."LISTNAME"='DB_TRN_CNT'))

There are several SQLs and two of them are mentioned above. How it could be possible referring remote table without DBLINK name? We tried to simulate this but not successful. DB Version is 11.2.0.3 and application is SAP. Also these SQLs are generating different child number. Thus we have thousands of child numbers against each SQLID. Please explain this behavior.

ora-12154 TNS could not resolve service name

August 14, 2014 - 7:25 am UTC

Reviewer: Nazmul Hoque from Bangladesh

Hi Dear,

I am not able connect oracle database 8i by below TNSNAMES.ORA under VPN

--------
GASLDATA.GASLSRVR.COM =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.200)(PORT = 1521))
)
(CONNECT_DATA = (SERVICE_NAME = GASLDATA))
)
-------------

H/Ever same is working fine in LAN. Please advise how solve in VPN.

Thnaks
Nazmul

ora-12154 TNS could not resolve service name

August 14, 2014 - 7:25 am UTC

Reviewer: Nazmul Hoque from Bangladesh

Hi Dear,

I am not able connect oracle database 8i by below TNSNAMES.ORA under VPN

--------
GASLDATA.GASLSRVR.COM =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.200)(PORT = 1521))
)
(CONNECT_DATA = (SERVICE_NAME = GASLDATA))
)
-------------

H/Ever same is working fine in LAN. Please advise how solve in VPN.

Thnaks
Nazmul

Connecting to AS400 using db link

December 23, 2014 - 11:59 pm UTC

Reviewer: A reader from 08831

I have created a db link from Oracle to DB2 ( I series).

CREATE PUBLIC DATABASE LINK REMSER.DB10 CONNECT TO "REMUSER" IDENTIFIED BY "rempwd" USING 'REMSER';


When I issue the statement as below , I get the results

" Select count(*) from bdata.tab1@REMSER.DB10;"


But when I issue the statement as below , I get an error

SQL Error: ORA-02019: connection description for remote database not found
02019. 00000 - "connection description for remote database not found"
*Cause:
*Action:

I checked the global_names , it is FALSE ( default) .

Similar setup in Oracle 10g works fine . What am I missing ?

Please advise.

Network Bandwidth Analysis

June 18, 2018 - 1:14 pm UTC

Reviewer: Arvind Mishra from Sweden

How to find that network bandwidth is problematic(or not) in case of a distributed/remote query?
Connor McDonald

Followup  

June 19, 2018 - 3:27 am UTC

Start with a simple trace - check to see how much time the network events are contributing to your total performance time:

SQL> select name from v$event_name
  2  where lower(name) like '%sql%net%';

NAME
--------------------------------------------------
SQL*Net message to client
SQL*Net message to dblink
SQL*Net more data to client
SQL*Net more data to dblink
SQL*Net message from client
SQL*Net more data from client
SQL*Net message from dblink
SQL*Net more data from dblink


Don't forget to take into account that "SQL*Net message from client" also includes the time you were not asking for anything from the database at all.

Provide query

June 22, 2018 - 8:35 am UTC

Reviewer: A reader

Following connor last valuable post. Could you please elaborate query to found out the delta tile sqlnet vs total time?

Data transfer over DBlink

July 17, 2020 - 9:39 am UTC

Reviewer: Rajasekhar from India

Hello Chris,
Could you please suggest better method that can be used over dblink for moving the data from One DB to Another DB.

Source db: Need to join two tables to get the result set that needs to transfer

option1: create a view at source db and querying that view from remote DB as below from remote

declare
cursor c is select * from view@dblink;
begin
loop
fetch c into collection limit 10k;
forall
insert into table;
end loop;
end;
option2: create a GTT in Source DB with result set and performing remote insert from same DB as below
declare
begin
insert into GTT (result set of joining the tables);
insert into remote table@dblink
select * from GTT;
end;

option3: writing a procedure with collection as out parameter and calling that procedure from remote DB
and use that collection for loading data in remote table.

can you help me in knowing pros and cons of above options and your suggestion from the options or out of the options ;)?
thanks in advance
Connor McDonald

Followup  

July 20, 2020 - 1:57 am UTC

They will be similar in performance, but for me, I would prefer the GTT for the simplicity.

And keeping mind with the simplicity... if you can do this

insert into GTT (result set of joining the tables);
insert into remote table@dblink


then perhaps you can even do this:

insert into remote table@dblink
select ... from join-of-local tables


DB Link usage with real time queries

July 29, 2020 - 10:09 am UTC

Reviewer: Oracle User from United Kingdom

Hi Tom,

Is it OK to use dblinks in real time queries? Can this potentially cause performance issues?

For e.g. something like below being executed several times from the front end.

SELECT A.*, B.*
FROM TABLEA A, TABLEB@DBLINK B
WHERE A.ID = B.ID
AND A.ID = 1;

Best Regards
Connor McDonald

Followup  

July 30, 2020 - 12:23 am UTC

Maybe :-)

Put simply a join can only happen on one database, so *one* of the databases will take on the responsibility of being "in charge". Let's call that database "X", which by the way, might be the *remote* database. The *other* database involved we will call "Y".

This means, for a cross database join, what will happen is one of:

1) - "X" will get the rows for table(s) on their node, and then for each row, will go across the link to find matching row(s) from "Y".

2) - "X" will get the rows for table(s) on their node, then request "Y" to get all the candidate rows for tables on its node, and then send them back to "X" where they will be joined locally.

So when it comes to tuning:

For (1) - if you have a lot of hops back and forth the network, you could be in trouble

For (2) - if the number of candidate rows *before* joining is large, you could be in trouble because that takes a long to ship across the network.


Join across dblink

July 31, 2020 - 6:36 am UTC

Reviewer: Rajasekhar from India

Hello Chris,

is it a good practice to use join conditions over dblink as below to get the latest data by joining two tables?