OA60394: AFTER OA59122 MAY SEE HIGH RATE OF FALSE CONTENTION FOR LOCK STR 20/10/30 PTF PECHANGE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• With the PTF for OA59122, there may be performance impact due to
  a higher false contention rate for a lock structure.  This
  higher rate of contention will drive a higher rate of XCF
  signalling requests to the locking group members (group name
  IXCLOxxx).
  In the case of the GRS ISGLOCK structure,  this also cause a
  performance impact to ENQ/DEQ processing resulting in higher
  rate of real ENQ contention due to higher rate of GRS local lock
  contention.
  
  
  VERIFICATION STEPS:
  1) Verify the PTF for OA59122 is installed.
  2) Compare a before and after picture of lock structure External
  Request/Contention rate in a RMF CF Activity report for the
  timeframe of the impact or with RMF III.  The contention rate
  should normally be .1% but with OA59122 we have seen it go as
  high as 87% in some intervals based on lock str activity.
  3) The false contention rate may show high for all
  connectors/systems even if the PTF for OA59122 is only installed
  on 1 or 2 systems in the sysplex. This is because the global
  lock mgr will send grants for false contention driving up the
  false contention rate for all local systems with interest in a
  resource.  Here is an example from a report showing the high
  false contention rate:
  
  
  EXTERNAL REQUEST
  CONTENTIONS
  
  REQ TOTAL     6356K
  REQ DEFERRED  1699K
  -CONT         1699K
  -FALSE CONT   1693K
  
  
  
  PE INFORMATION:
  USERS AFFECTED:
  All users with OA59122 PTF UJ03932 or UJ03933 installed
  supporting connectors to lock structures.
  
  APAR OA59122 addressed a problem where locking connectors become
  message-isolated when a burst of IXLLOCK requests releases a
  large number of globally managed resources causing the XES
  global management of those resources to end suddenly.
  
  USER IMPACT:
  APAR OA59122 fixed the problem it reported but introduced a new
  problem.
  
  APAR OA59122 better handles bursts of IXLLOCK requests that
  cause global management of a large number of resources to end
  avoiding becoming message-isolated  (and associated MSGIXC638I
  and MSGIXC645E from being issued), and avoiding exploiter delays
  (avoiding ABENDS026 RSN08118001 from being issued) due to the
  associated processing. It introduces a performance impact due to
  a higher rate of false contention for lock structures.
  

Local fix

• BYPASS/CIRCUMVENTION:
  Verify the lock structure is sized correctly to minimize impact
  of OA59122 using the CFSIZER:
  https://www.ibm.com/support/pages/cfsizer
  
  RECOVERY ACTION:
  Back off the PTF for OA59122 if possible until OA60394 PTF is
  available, or apply the ++APAR for OA60394.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * Users who are running in a Parallel Sysplex environment      *
  * making use of coupling facility (CF) lock structures for     *
  * sysplex-scope serialization functions. In particular those   *
  * with APAR OA59122 installed.                                 *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * After applying PTFs for OA59122, a higher rate of false      *
  * contention may be encountered when XES lock resources are no *
  * longer in contentention and XES global management of the     *
  * resources does not end in a timely manner. The high false    *
  * contention rates may be observable through the Resource      *
  * Measurement Facility (RMF) and lead to performance impacts   *
  * due to unnecessary XES signal activity to the XES locking    *
  * group members.                                               *
  *                                                              *
  * SYSPLEXDS                                                    *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * PTFs should be applied to all systems in the sysplex via     *
  * rolling IPL.                                                 *
  ****************************************************************
  With OA59122 applied, when XES locking resources are no longer
  in contention, the ending of XES global management is paced to
  help XES locking group members avoid being message isolated.
  Subsequent non-contention XES locking requests processed before
  XES global management ends can elongate the time before XES
  global management ends. This leads to unnecessary XES signal
  activity causing high false contention rates and associated
  impacts. In the case of GRS ENQ/DEQ processing with the ISGLOCK
  structure, processing associated with the additional XES signal
  activity contributes towards additional GRS local lock
  contention and a higher rate of real GRS ENQ contention.
  

Problem conclusion

• Modifications made to end XES global management of resources in
  a more timely manner when the ending of XES global management is
  being paced and subsequent non-contention XES locking requests
  are encountered.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

• ×**** PE21/07/28 FIX IN ERROR. SEE APAR OA61848  FOR DESCRIPTION
  

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UJ04727 UJ04728

Modules/Macros

• IXLR1GLB
  

Fix information

• Fixed component name

  CROSS SYS.EXT.S

• Fixed component ID

  5752SCIXL

Applicable component levels

• R7B0 PSY UJ04727

     UP21/01/20 P F101 ­

• R7C0 PSY UJ04728

     UP21/01/20 P F101 ­

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.