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Connor McDonald

Thanks for the question.

Asked: May 22, 2016 - 5:32 am UTC

Last updated: May 27, 2016 - 12:27 am UTC

Version: 11g

Viewed 1000+ times

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Ref. :- https://docs.oracle.com/cd/E11882_01/server.112/e40540/tablecls.htm
See Figure :- 2.6

Suppose We create cluster on emp and dept. and cluster is clus_emp_dept and common column is dept_no.
Now question is

1. suppose cluster allocate continuous memory or not?
2. suppose cluster created and i inserted data then, I also reinsert data on emp table then what happen below situation
2.1 :- Insert row in emp table and emp_no is 20.
Here I assume that row insert.
2.2 :- Now I insert a emp with emp_no is 30 then how to insert?
Here I assume that emp_30 insert after block of emp_no 20 or i wrong?
2.3 :- Once again I insert emp_no 20 then what happen?
Here I assume that To allocate block after Block of emp_no 20 and before emp_no 30 or I'm wrong?

Can you explain me above situation , how cluster table work?

and Connor said...

Some good info here

https://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:6369500346363001

But the concept is relatively straihtforward

If you give me a a department row (deptno=100), and some employee records which all belong to deptno=100, then we are going to *try* to store these records together.

The emphasis here is *try*...if you have 50,000 employees all in deptno=100, then obviously we are not going to be able to store all 50,000 on the same block as the department row for deptno=100. We will have to use multiple blocks, and link them together.

But if its just a small number, then there's a good chance, they'll all sit on the same block as the department row, hence making joins more efficient.

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Comments

A reader, May 23, 2016 - 3:50 am UTC

How to create cluster on existing table?
Connor McDonald
May 23, 2016 - 6:12 am UTC

You can't directly. You could use DBMS_REDEFINITION

SQL> create cluster t_clust (a integer, b integer);

Cluster created.

SQL> create table t_new ( a int primary key, b int, z int )
  2  cluster t_clust(a,b);

Table created.

SQL>
SQL> create index t_clust_ix on cluster t_clust;

Index created.

SQL>
SQL> create table t ( a int primary key, b int, z int );

Table created.

SQL>
SQL> insert into t
  2  select rownum , rownum, rownum
  3  from dual
  4  connect by level <= 1000;

1000 rows created.

SQL>
SQL> commit;

Commit complete.

SQL>
SQL>
SQL> exec dbms_redefinition.can_redef_table(user, 't');

PL/SQL procedure successfully completed.

SQL>
SQL> exec dbms_redefinition.start_redef_table(user, 't', 't_new');

PL/SQL procedure successfully completed.

SQL>
SQL> exec dbms_redefinition.finish_redef_table(user, 't', 't_new');

PL/SQL procedure successfully completed.

SQL>
SQL> select table_name, cluster_name
  2  from user_tables
  3  where table_name = 'T';

TABLE_NAME                     CLUSTER_NAME
------------------------------ ------------------------------
T                              T_CLUST

1 row selected.

SQL>
SQL>


A reader, May 25, 2016 - 9:39 am UTC

exec dbms_redefinition.start_redef_table(user, 't', 't_new');

but table or view does not exists
Connor McDonald
May 26, 2016 - 3:54 am UTC

Paste the output of the entire script, just like I do.

A reader, May 26, 2016 - 11:58 am UTC 

step 1
------

create table dept
(
  dno number(6) primary key,
  dname varchar2(20),
  location varchar2(20)
)

step 2
------

create table emp
(
  eno number(6) primary key,
  dno number(6) references dept (dno),
  ename varchar2(20),
  job varchar2(20),
  mobileno number(10)  
)

step 3
------

begin
  for i 1 in 100000
  loop
      insert into dept values(i, dbms_random.string('U',20),dbms_random.string('U',20))
  end loop;
end;
/ 

begin
  for i in 1 .. 400000
  loop
      insert into emp values(i,dbms_random.values(1,100000), dbms_random.string('A',20),dbms_random.string('U',20),dbms_random.values(9009009009,9999999999));
      commit;
  end loop;
end;
/  


step 4
------

create cluster cl_emp_dept (dno number(4));
 
create index cl_ind_emp_dept on cluster cl_emp_dept;

step 5
------

begin
  dbms_redefinition.can_redef_table('user1', 'dept');
end; 

step 6
------

begin
  dbms_redefinition.start_redef_table('user1', 'dept','dept_new');
end; 



=========================================================ror :- step 6
============================================================
Error starting at line 1 in command:
begin
  dbms_redefinition.start_redef_table('user1', 'dept','dept_new');
end; 
Error report:
ORA-00942: table or view does not exist
ORA-06512: at "SYS.DBMS_REDEFINITION", line 52
ORA-06512: at "SYS.DBMS_REDEFINITION", line 1646
ORA-06512: at line 2
00942. 00000 -  "table or view does not exist"
*Cause:    
*Action:
==========================================================================

Connor McDonald
May 27, 2016 - 12:27 am UTC

Not "user1" in quotes, but just 'user' the *function* which returns who you are currently connected as:

So instead of:

dbms_redefinition.start_redef_table('user1', 'dept','dept_new');

use

dbms_redefinition.start_redef_table(user, 'dept','dept_new');

Or, if the dept table is in another schema (say SCOTT) you would do:

dbms_redefinition.start_redef_table('SCOTT', 'dept','dept_new');
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