Switching on/off bug fixes / patches

From 10g onwards there is a hidden parameter _fix_control that can be used to turn off/on a particular bug fix. (Be sure, this is hidden parameter and as usual note changing hidden parameters must be done after consulting Oracle)

For example, a patch 5483301 has been recently applied to the database using opatch, and after that you  have seeing some issues, you want to determine the root cause, but you cannot rollback the patch to test, in such scenarious this hidden parameter can come in handy.

Given the same scenario, First check the patch registered and enabled. (replace your patch number)

SQL> select bugno, value, description, optimizer_feature_enable from v$system_fix_control where bugno=5483301;


BUGNO           VALUE      DESCRIPTION                          OPTIMIZER_FEATURE_ENABLE

5483301          1             Use min repeat count                    10.2.0.4

                                       in freq histogram to compute the density

As my patch is listed here, I can disable and determine that the issue happening in the database is because of this patch or not. to do same.

alter system set "_fix_control"='5483301:off' scope=both;
or for the session
alter session set "_fix_control"='5483301:off';

SQL> select bugno, value, description, optimizer_feature_enable from v$system_fix_control where bugno=5483301;


BUGNO VALUE DESCRIPTION OPTIMIZER_FEATURE_ENABLE

5483301 0 Use min repeat count 10.2.0.4

in freq histogram to compute the density

Now try to reproduce the issue you have. Once you determine the issue is because of this patch , you can let the bug fix off in the database or let it enable back.

alter system set "_fix_control"='5483301:on' scope=both;
or for the session
alter session set "_fix_control"='5483301:on';

Note:- provided only for educational purposes only, not to try in production systems unless you are sure what you are doing.

-Thanks

Geek DBA