PH39316: MQ CHIN HANGS WHILE MANY CHANNELS RETURN A TCP STATE OF CLOSE_WAIT WITHIN A QUEUE SHARING GROUP ( QSG )

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• User reported that the MQ CHIN appeared hung while many
  channels remained in an unexpected TCP state indefinitely. Some
  channels retained an MQ state of PAUSED while SENDER channels
  were in a BINDING state, but never were able to start.
  Development analysis indicates that there is an issue whereby,
  if, within a QSG, channels are defined for AdoptMCA, this can
  result in semaphore contention. If a shared RCVR is started on
  QM2 (while an instance of that RCVR is already RUNNING on QM1)
  then, when the channel adoption code is driven, this can cause
  CSQXSEM to request the XSCS semaphore, without it being
  released. If, then, other shared channels need to be started,
  their processing will be blocked behind the first XSCS
  semaphore that is still held, leading to a build-up of this
  contention. Symptoms can include reason codes : MQRC 2002 (
  MQRC_ALREADY_CONNECTED ) and MQRC 2271 ( MQRC_CONN_TAG_IN_USE
  ). Dump report CHSTATUS=4 can be used to determine the count of
  XSCS entries in the semaphore table.
  

Local 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: The Adopt MCA function may cause the    *
  *                      channel initiator to hang for a queue   *
  *                      manager in a QSG.                       *
  ****************************************************************
  When using shared channels, Adopt MCA failure is possible
  due to timer expiry preventing the channel from being canceled.
  
  This problem relies on adoption being attempted close to the
  timer popping.
  

Problem conclusion

• The Adopt MCA logic has been rectified.
  

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:

  UI82802 UI82803 UI82804

Modules/Macros

• CSQXRCSI CSQXRMMQ CSQXSCAN
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI82804

     UP22/10/25 P F210

• R200 PSY UI82803

     UP22/10/22 P F210

• R300 PSY UI82802

     UP22/10/22 P F210

Fix is available

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