PH64495: MQ Z/OS: HIGH LOCAL LOCK CONTENTION FOR THE CHIN JOB

APAR status

• Closed as program error.

Error description

• An IBM MQ CHIN (channel initiator) is running with a large
  number of SVRCONN client channels with the SHARECNV channel
  attribute configured to be greater than zero.
  .
  Even with APARs PH37062 and PH52586 applied, performance can be
  impacted by a high level of local lock (LOCL) contention.
  .
  A couple of places where this contention is evident is in
  IPCS SYSTRACE PERFDATA output for an SVC dump or in SMF
  record types 72.5 (Serialization Delay) and 98.1 (Workload
  Interaction Correlatoror or WIC).
  .
  The systrace also has many EVENTS calls from CSQXACNO and
  associated POST calls.
  

Local fix

• N/A
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 4 Modification 0.                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: When many SVRCONN client channels with  *
  *                      SHARECNV > 0 are active and performing  *
  *                      MQGET operations with wait intervals,   *
  *                      the internal async consume notification *
  *                      mechanism may generate excessive local  *
  *                      lock contention due to the high number  *
  *                      of z/OS POST SVC calls. This manifests  *
  *                      as high CPU usage and performance       *
  *                      degradation, visible through            *
  *                      IPCS SYSTRACE showing numerous EVENTS   *
  *                      and POST calls. Should the events table *
  *                      reach its maximum capacity, an S502     *
  *                      abend may also occur under certain      *
  *                      circumstances if the event table        *
  *                      becomes full.                           *
  ****************************************************************
  High local lock contention in the channel initiator address
  space.
  

Problem conclusion

• Processing has been adapted to significantly reduce the need
  for additional z/OS POST SVC calls when messages arrive on
  queues. The work that was performed by the CSQXACNO module has
  been made more efficient, reducing local lock contention. This
  new processing is not enabled by default. After applying the
  associated PTF, you will need to contact IBM Service to request
  the instructions to enable the new function.
  

Temporary fix

Comments

APAR Information

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

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

  UO07843

Modules/Macros

• CSQIRECP CSQM1P1W CSQMACNO CSQMCHKQ CSQMGET  CSQMLEPL CSQMOAOH
  CSQMPRH2 CSQMSTRT CSQXJST  CSQXRSTM
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels