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Tom Kyte

Thanks for the question, Andre .

Asked: December 19, 2000 - 2:06 pm UTC

Last updated: July 06, 2010 - 10:53 am UTC

Version: 8.1.6

Viewed 1000+ times

You Asked

I´ve recently been aware of the undocumented init.ora parameters -- those begining with "_" (underline). There is list of them in a book available on the market. In which situation could (or should) we, mortal DBAs, use them ? Do you remeber any specific situation where it can be necessary to take advantage of them ? In what aspects do they differ from the documented ones ? Can we regularily use them in any init.ora file ? Can you give me an example ?

Thanks !

and Tom said...

In my development database, i use only one -- _TRACE_FILES_PUBLIC. That makes trace files readable by all, not just the DBA group. In my real database, I use none. On my development database I want my developers (well, i demand it actually) to use sql_trace+timed_statistics and tkprof frequently -- hence they need to be able to read the trace files.


In general -- you will only use these undocumented parameters at the request of Oracle Support. The use of them can be damaging to a database and their implementation can and will change from release to release.


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oracle support

liz, April 28, 2002 - 8:30 am UTC

helllo tom
i need more underestanding of the folowing

In general -- you will only use these undocumented parameters at the request of
Oracle Support. The use of them can be damaging to a database and their
implementation can and will change from release to release.




Tom Kyte
April 28, 2002 - 10:08 am UTC

Hmmm, I don't know how to make it more clear.

Basically I'm saying:

DO NOT use undocumented parameters that begin with underscores.

If you do, you may damage your database.

Many of these parameters cause side effects that if you are not aware of them, could seriously damage your database.

Until a parameter is documented, it is unsafe. Use at your own risk.

parameters

mo, December 23, 2002 - 9:56 am UTC

Tom:

Does "Select * from v$parameter" give you all the
parameters defined for that database? Are those the same defined in the init.ora paramete file?

2. how you query the session parameters? any v$ for that?

Thank you,

Tom Kyte
December 23, 2002 - 11:15 am UTC

yes, maybe.

many of the session parameters modify your view of the v$parameter table. change your sort_area_size for example and see.

How to list the undocumented parameters....

Ma$e, January 27, 2005 - 1:53 pm UTC

Hi Tom:

Could you please provide me the method to list all undocumented parameters?

Thanks


Ma$e

Tom Kyte
January 27, 2005 - 2:03 pm UTC

why, you won't be changing them.... (you should have seen that coming, based on the pre-existing text....)

you can always google

oracle undocumented parameters



Here is the SQL

Rajesh, January 28, 2005 - 3:09 am UTC


SELECT
a.ksppinm "Parameter",
a.ksppdesc "Description",
b.ksppstvl "Session Value",
c.ksppstvl "Instance Value"
FROM
x$ksppi a,
x$ksppcv b,
x$ksppsv c
WHERE
a.indx = b.indx
AND
a.indx = c.indx
AND
a.ksppinm LIKE '/_%' escape '/'
/


Tom Kyte
January 28, 2005 - 7:24 am UTC

borrowed straight from the first link google returns when you did the search....

just remember to consider the source

Well, Thanks Tom

Rajesh, January 30, 2005 - 11:39 pm UTC

All i needed was a response from you Tom!! and I am glad !

(will nomore behave silly!)

the source for the above SQL ::

</code> http://www.dba-oracle.com/oracle_faq/faq_dba_9i_hidden_parms.htm <code>


Tom Kyte
January 31, 2005 - 8:08 am UTC

(just remember to consider the source -- didn't need to attribute it, that wasn't what I was after)

Well, Got it now...

Rajesh, May 19, 2005 - 3:01 am UTC

Finally, after 6 months of extensive reading here(and elsewhere), I realised the blunder I made :-)

Alex, May 24, 2010 - 9:02 am UTC

Tom,

One of our DBAs set some undocumented parameters because apparently they are set for our Oracle Applications suite, and therefore are ok because basically Oracle is ok with them by implication. Can you tell me how dangerous these are, two I don't like the looks of just by the names (fast full scan, view merging, I'd like Oracle to be able to do those if it feels like it)

SQL> select name, value from v$parameter where isdefault = 'FALSE';

NAME                                     VALUE
---------------------------------------- ------------------------------------------------------------
processes                                1000
sga_max_size                             4294967296
sga_target                               4294967296
control_files                            /ocms06t/data/control01.ctl, /ocms06t/logs/control02.ctl, /o
                                         cms06t/backup/control03.ctl

control_file_record_keep_time            45
db_block_size                            8192
compatible                               10.2.0.2.0
log_archive_dest_1                       LOCATION=/ocms06t/logs
log_archive_format                       %t_%s_%r.dbf
db_file_multiblock_read_count            16
undo_management                          AUTO
undo_tablespace                          UNDOTBS1
undo_retention                           259200
_kks_use_mutex_pin                       TRUE
remote_login_passwordfile                EXCLUSIVE
db_domain                                LMIG.COM
dispatchers                              (PROTOCOL=TCP) (SERVICE=OCMS06TXDB)
job_queue_processes                      10
_system_trig_enabled                     TRUE
cursor_sharing                           EXACT
background_dump_dest                     /oracle/product/admin/OCMS06T/bdump
user_dump_dest                           /oracle/product/admin/OCMS06T/udump
core_dump_dest                           /oracle/product/admin/OCMS06T/cdump
audit_file_dest                          /oracle/product/admin/OCMS06T/adump
audit_trail                              DB, EXTENDED
db_name                                  OCMS06T
open_cursors                             300
_sort_elimination_cost_ratio             5
_b_tree_bitmap_plans                     FALSE
_fast_full_scan_enabled                  FALSE
_sqlexec_progression_cost                2147483647
_like_with_bind_as_equality              TRUE
pga_aggregate_target                     1073741824
_gby_hash_aggregation_enabled            FALSE
optimizer_secure_view_merging            FALSE

35 rows selected.


Tom Kyte
May 24, 2010 - 1:10 pm UTC

if Oracle support told you to set them, then set them. If they did not, then do not.

understanding

Anurada, June 25, 2010 - 2:12 pm UTC

what are u saying there is no formatting in this site,, either wats asking anyone and what Mr. tom u r telling its not clear,, there shud be a proper formatting of this site then it wud be clear what is the question and what telling tom about that question..

there shud be no discussion regarding asking question and during answering ..

thanks dnt delete my post i think there is nthing wrong what m saying...

ragards
Tom Kyte
July 06, 2010 - 10:53 am UTC

"U" isn't available, "U" is dead as far as I know. Look it up, it is true.

http://en.wikipedia.org/wiki/U_of_Goryeo



I don't follow what you are saying at all - not just because of the ambiguous abbreviations frequently used by 12 year olds when texting each other - but because what you wrote here has no bearing on anything written on this page at all.