Enhancement to obsolete parent cursors if VERSION_COUNT exceeds a threshold (文档 ID 10187168.8)

Bug 10187168  Enhancement to obsolete parent cursors if VERSION_COUNT exceeds a threshold

 This note gives a brief overview of bug 10187168. 
 The content was last updated on: 28-JUN-2013
  Click here for details of each of the sections below.
 There are additional notes on this bug in  Note:296377.1

Affects:

Product (Component)	Oracle Server (Rdbms)
Range of versions believed to be affected	Versions BELOW 12.1
Versions confirmed as being affected	11.2.0.2 11.2.0.1 11.1.0.7
Platforms affected	Generic (all / most platforms affected)

  Note that this fix can cause / expose the problem described in Bug:10264680 

 Note that this fix can cause / expose the problem described in Bug:11699057 

 Note that this fix can cause / expose the problem described in Bug:11069199 

 Note that this fix can cause / expose the problem described in Bug:14585499 

Fixed:

This issue is fixed in

12.1.0.1 (Base Release) 11.2.0.3 (Server Patch Set) 11.2.0.2.2 Database Patch Set Update 11.2.0.2 Bundle Patch 6 for Exadata Database 11.2.0.1 Bundle Patch 12 for Exadata Database 11.1.0.7.7 Database Patch Set Update 11.2.0.2 Patch 3 on Windows Platforms 11.1.0.7 Patch 38 on Windows Platforms

Symptoms:	Related To:
Code Improvement Mutex Contention Shared Pool Affected	V$SQLAREA _cursor_obsolete_threshold _cursor_features_enabled

Description

High version counts can lead to mutex contention and other contention
issues , even if the high version count is for a valid reason.
 
This bug is a marker for an enhancement request to allow parent
cursors to be obsoleted if the version count exceeds a set threshold.
It introduces the new hidden parameter "_cursor_obsolete_threshold"
which should only be set under the guidance of Oracle support.
(In interim patches event 106001 is used instead of "_cursor_obsolete_threshold")
 
This fix *does not* fix the reason for the high version count.
It only helps to mitigate the effects. 
It is highly recommended to identify the reason for the high version count
(following Note:296377.1) even if this fix reduces its impact.
 
Note: One off patches including this fix use event 106001
      to control the cut off point 
      ie: event 106001 is used instead of "_cursor_obsolete_threshold"
 
      To enable the fix "_cursor_features_enabled" needs to be set 
      to a special value that depends on the patch level, and then 
      either "_cursor_obsolete_threshold" (or event 106001) must also
      be set the the desired threshold level. 

 
      IMPORTANT: As with any hidden parameters / events the values used should
       be reviewed for correctness when upgrading or patching to a later release.
       This is particularly important for this fix as values of "_cursor_features_enabled"
       have different meanings in different DB versions.
      
      Also see bug 10264680 which alters the fixed view V$SQLAREA
      to dis-count cursors that have been obsoleted, and bug 11699057
      which may return duplicate rows from V$SQLSTATS if this fix
      is active, and bug 11069199 which can occur if this fix is 
      present. Also bug 14585499 can occur if this fix is activated.
 
Workaround
  None other than address the cause of the lack of sharing.
 

Further details on this issue can be found in Note:296377.1

Please note: The above is a summary description only. Actual symptoms can vary. Matching to any symptoms here does not confirm that you are encountering this problem. For questions about this bug please consult Oracle Support.

References

Bug:10187168 (This link will only work for PUBLISHED bugs)
Note:245840.1 Information on the sections in this article

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