PI89568: MQ FOR Z/OS: THE CHIN JOB LOOPS READING SYSTEM.CHANNEL.SYNCQ RECORDS FOR A CHANNEL WITH MULTIPLE CLUSTER TRANSMIT QUEUES

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• High CPU in the CHIN job is observed.  It started after a
  RESOLVE CHANNEL command was done for an indoubt cluster channel
  that had been receiving CSQX507E channel is in-doubt.
  
  A CHIN trace has repetitive entries:
  Entry   15:28:53.371106  rrxReadSync
  Entry   15:28:53.371107  CSQXSEM Semaphore Processing
  Exit    15:28:53.371107  CSQXSEM Semaphore Processing
  Entry   15:28:53.371108  CSQXSEM Semaphore Processing
  Exit    15:28:53.371109  CSQXSEM Semaphore Processing
  Entry   15:28:53.371109  MQGET   Get Message
  Entry   15:28:53.371110  CSQXSRVR Service Requester
  Exit    15:28:53.371119  CSQXSRVR Service Requester
  Exit    15:28:53.371120  MQGET   Get Message
  Entry   15:28:53.371121  MQGET   Get Message
  Entry   15:28:53.371122  CSQXSRVR Service Requester
  Exit    15:28:53.371205  CSQXSRVR Service Requester
  Exit    15:28:53.371206  MQGET   Get Message
  Exit    15:28:53.371207  rrxReadSync
  
  The MQGET is for SYSTEM.CHANNEL.SYNCQ.  The records being
  returned alternate between two messages with the same cluster
  channel name but different transmission queue names.
  
  There is an issue with channel sync records and multiple
  cluster transmit queues if a REFRESH CLUSTER command is issued
  while the cluster sender channel is indoubt. This can result in
  multiple indoubt sync records on the SYSTEM.CHANNEL.SYNCQ with
  different transmit queues in the records. In this case, during
  the RESOLVE CHANNEL command, if the cluster channel definition
  has a different transmit queue than an indoubt sync record, a
  loop condition may occur when the SYNCQ is being read.
  
  Note that a REFRESH CLUSTER should be used in rare
  circumstances.
  
  Additional Symptom(s) Search Keyword(s):
  Performance
  CSQXRSYN
  

Local fix

• If the loop occurs, a CSQ4SUTL utility may be provided that
  will help clear bad records from SYSTEM.CHANNEL.SYNCQ.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 8       *
  *                 Release 0 Modification 0.                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: Errors occur when using CSQUTIL to      *
  *                      switch the transmit queue used by a     *
  *                      CLUSSDR channel. These can include:     *
  *                       - duplicate syncq records              *
  *                       - loops when resolving indoubt clussdr *
  *                         channels                             *
  *                       - incorrect indoubt resolution for     *
  *                         clussdr channels                     *
  ****************************************************************
  When CSQUTIL is used to issue the SWITCH CHANNEL command in
  order to make a pending xmitq switch for a cluster sender
  channel active, it causes the transmit queue name to be
  updated in sync records on SYSTEM.CHANNEL.SYNCQ, and in the
  channel initiators live copies of these records.
  However, when the channel is indoubt, the indoubt record on the
  sync queue is not updated, leading to a loop if RESOLVE CHANNEL
  is used to resolve the indoubt state.
  In addition, a chaining error when updating the live sync record
  can cause the live sync record to be lost in some circumstances,
  leading to duplicate records being created for the channel, and
  in the case of indoubt channels, the resolution of the indoubt
  state being performed incorrectly.
  

Problem conclusion

• When switching cluster transmit queue using CSQUTIL, any indoubt
  records for the channel are now updated, and the chaining error
  when processing the live record is corrected.
  

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:

  PH07185 UI61200

Modules/Macros

• CSQMCTQS CSQXRSYN
  

Fix information

• Fixed component name

  IBM MQ Z/OS V8

• Fixed component ID

  5655W9700

Applicable component levels

• R000 PSY UI61200

     UP19/02/28 P F902 ¢

Fix is available

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