Oracle 11g : Poor Performance Accessing V$SESSION_FIX_CONTROL

PeopleSoft HCM, Financials/SCM 9.x customers may have to patch their Oracle database server with RDBMS patch 9699654. Rest of the Oracle customers: read the symptoms and decide.

In couple of PeopleSoft deployments it is observed that the following SQL is the top query when all queries are sorted by elapsed time or CPU time. 11.2.0.1.0 is the Oracle database server version.


SELECT VALUE FROM V$SESSION_FIX_CONTROL WHERE BUGNO = :B1 AND SESSION_ID = USERENV('SID')

The target query is being executed thousands of times. The poor performance is due to the lack of a proper index. Here is the explain plan that exhibits the performance issue.

-------------------------------------------------------------------------------
| Id  | Operation	 | Name       | Starts | E-Rows | A-Rows |   A-Time   |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |	      |      1 |	|      1 |00:00:00.02 |
|\*  1 |  FIXED TABLE FULL| X$QKSBGSES |      1 |      1 |      1 |00:00:00.02 |
-------------------------------------------------------------------------------

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

   1 - filter(("BUGNO_QKSBGSEROW"=:B1 AND
	      "SID_QKSBGSEROW"=USERENV('SID') AND "INST_ID"=USERENV('INSTANCE')))

20 rows selected.

Oracle Corporation accepted this behavior as a bug and agreed to fix in Oracle RDBMS 12.1. Meanwhile an RDBMS patch was made available to the customers running 11.2.0.1 or later. 9699654 is the bug# (Bad performance of V$SESSION_FIX_CONTROL query) - so, Solaris SPARC customers can download the RDBMS patch 9699654 directly from the support web site. Customers on other platforms: please search the bug database and support web site with appropriate keywords.

After applying the RDBMS patch 9699654, the optimizer was using an index and the query performance was improved as expected. Also the target SQL query was no longer the top SQL - in fact, no references to this particular query were found in the AWR report. The new explain plan is shown below.

----------------------------------------------------------------------------------------------
| Id  | Operation               | Name               | Starts | E-Rows | A-Rows |   A-Time   |
----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT        |                    |      1 |        |      1 |00:00:00.01 |
|\*  1 |  FIXED TABLE FIXED INDEX| X$QKSBGSES (ind:1) |      1 |      1 |      1 |00:00:00.01 |
----------------------------------------------------------------------------------------------

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

   1 - filter(("BUGNO_QKSBGSEROW"=:B1 AND "SID_QKSBGSEROW"=USERENV('SID') AND
              "INST_ID"=USERENV('INSTANCE')))

20 rows selected.
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