PH37062: MQ Z/OS: PERFORMANCE ISSUES WITH HIGH WORKLOAD ON SVRCONN CHANNELS WITH SHARECNV ENABLED

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• In a dump, system trace shows a large amount of LOCL (local)
  lock contention and thousands of POST and EVENTS SVCs for the
  CHIN job. The CHIN is running with a large number of SVRCONN
  client channels with the SHARECNV channel attribute configured
  to be greater than zero.
  
  Development has identified improvements that can be made to the
  efficiency of this code to:
  - greatly reduce the number of times that ECBs are posted in a
  high-workload environment
  - make other optimizations to MQ's use of the z/OS EVENTS table
  to significantly reduce the overhead when processing large
  numbers of events.
  
  It is possible that the described contention exposed a timing
  window that allowed an ABEND0C4 in CSQXACNO after label
  ADD_EVENT_LOCK_LOOP.  The abend caused some channels to hang.
  If the hung channel holds an object handle on the queue, a
  subsequent application that requires exclusive use of the queue
  can receive MQRC 2042 MQRC_OBJECT_IN_USE.
  

Local fix

• Using SHARECNV(0) might avoid some of the symptoms in this
  APAR, but it will also remove  functionality such as:
    - Bi-directional heartbeats
    - Administrator stop-quiesce
    - Read-ahead
    - Asynchronous-consume by client applications
  Reference
  https://www.ibm.com/docs/en/ibm-mq/9.1?topic=cbdvmmcqm-mqi-clien
  t-default-behavior-client-connection-server-connection-channels
  
  You will need to test the setting to see which offers the best
  option while waiting to apply the fix.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0, Release 2          *
  *                 Modification 0 and Release 3 Modification 0. *
  ****************************************************************
  * PROBLEM DESCRIPTION: Performance issues with high workload   *
  *                      on SVRCONN channels when SHARECNV       *
  *                      enabled.                                *
  ****************************************************************
  Performance issues with high workload
  on SVRCONN channels when SHARECNV
  enabled.
  

Problem conclusion

• Process flow in the  asynchronous consumer notifier program
  csqxacno has been simplified to reduce contention and improve
  performance under high workload conditions.
  

Temporary fix

Comments

•  **** PE23/02/13 FIX IN ERROR. SEE APAR PH52586  FOR DESCRIPTION
   **** PE23/02/13 FIX IN ERROR. SEE APAR PH52586  FOR DESCRIPTION
   **** PE23/02/13 FIX IN ERROR. SEE APAR PH52586  FOR DESCRIPTION
  ×**** PE23/02/14 FIX IN ERROR. SEE APAR PH52586  FOR DESCRIPTION
  

APAR Information

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

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

  UI83494 UI83495 UI83496

Modules/Macros

• CSQXACNO
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI83496

     UP22/12/23 P F212

• R200 PSY UI83495

     UP22/12/23 P F212

• R300 PSY UI83494

     UP22/12/23 P F212

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.