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Bug 9239863  Excessive "library cache:mutex X" contention on hot objects

 This note gives a brief overview of bug 9239863. 
 The content was last updated on: 28-JUN-2013
  Click here for details of each of the sections below.

Affects:

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

Fixed:

This issue is fixed in
  • 12.1.0.1 (Base Release)
  • 11.2.0.2 (Server Patch Set)
  • 11.2.0.1 Bundle Patch 6 for Exadata Database

Symptoms:

Related To:

  • Code Improvement
  • Mutex Contention
  • Waits for "library cache: mutex X"
  • _kgl_hot_object_copies
  • _KGL_DEBUG

Description

When there is *true* contention on a specific library cache object 
then performance of the instance might be bottlenecked on 
"library cache: mutex X" waits for that object.
 
This fix is really an enhancement to allow specific objects
which are known to exhibit high contention to be marked such
that the contention can be reduced (by holding multiple 
copies of the object in the library cache).
 
Rediscovery Notes:
 The following query may help identify objects being
 accessed heavily:
  select KGLNAOBJ, KGLNAOWN, KGLHDNSP,  KGLOBTYP, KGLOBT23, KGLOBT24
    from x$kglob where KGLOBT23 > 1000000 or KGLOBT24 > 1000000
   order by  KGLOBT24;
 
Note: 
 This fix requires special configuration via hidden parameters
 to have any effect. The fix should only be enabled under the
 guidance of Oracle Support.

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:9239863 (This link will only work for PUBLISHED bugs)
Note:245840.1 Information on the sections in this article
 
 

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