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PH27898: MQ MEMORY LEAK IN PUBSUB TOPIC SCAVENGER ROUTINE

A fix is available

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • The original problem description from APAR IT15770 for WebSphere
    MQ and IBM MQ for multi-platforms:
    ----------------------------------------------------------------
    Available memory on the system may either become exhausted or
    may be seen to be increasing in an unbounded manner.
    
    Further investigation may show that the Java JVM process and the
    MQ amqzmuc0 process are using a large amount of memory.
    --------------------------------------------------------
    
    Symptoms for this APAR for IBM MQ for z/OS:
    ------------------------------------------
    - The leak of 64 bit storage can be observed by a continually
      decreasing amount of free "above bar" storage in the
      following message:
    
      CSQY220I CSQSCTL Queue manager storage usage:
      local storage: used nnnnMB, free nnnnMB: above bar: used nGB,
      free nnnnMB
    
    - If the above-the-bar storage for MQ (capped by MEMLIMIT) is
      exhausted, the following message will occur:
    
      CSQY227E CSQSHGMN Unable to allocate storage
      above the bar using IARV64, RC=00000008, reason=4A001620
    
    - Dumps:
    
      ABN=5C6-00A30042,U=userid,C=MQ900.900.SMC -CSQSHGMN,
      M=CSQGFRCV,LOC=CSQSLD1 .CSQSHGMN+00001140
    
      ABN=5C6-00E7014F,C=MQ900.900.CHIN,R=E7404040,
      LOC=CSQXADPM.CSQXADPM+05274
    
      In the output of
        LISTHIMO asid
        (where 'asid' is the queue manager's hexadecimal ASID)
      the 64bit MOMB blocks point to storage with TPFX eyecatchers.
      The PFX+1C points to R14 for CSQTOGMN's caller. The nearest
      eyecatcher going back is kqiTopicCreateSubscriberLink. That
      routine is in CSECT CMQXKTPU in load module CSQTOPLM.
    

Local fix

  • If it is possible to increase MEMLIMIT for the MSTR job, that
    will increase the time before storage is exhausted.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
    *                 Release 0 Modification 0.                    *
    ****************************************************************
    * PROBLEM DESCRIPTION: Users with large number of topic nodes  *
    *                      in their topic tree may run out of      *
    *                      above the bar storage. The following    *
    *                      message may be seen:                    *
    *                      CSQY227E CSQSHGMN Unable to allocate    *
    *                      storage above the bar using IARV64,     *
    *                      RC=00000008, reason=4A001620            *
    ****************************************************************
    The topic scavenger routine, which checks and reclaims the space
    used by dynamic topic nodes, does not correctly free all
    allocated storage for nodes in the topic tree. On systems with
    a large number of topic nodes in their topic tree this can
    result in a rise in reported storage usage in message CSQY220I,
    and can lead to exhaustion of above-the-bar storage.
    

Problem conclusion

  • The code has been corrected to free all storage associated with
    a topic node once it is removed from the tree.
    

Temporary fix

  • 
    

Comments

  • 
    

APAR Information

  • APAR number

    PH27898

  • Reported component name

    IBM MQ Z/OS V9

  • Reported component ID

    5655MQ900

  • Reported release

    000

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2020-07-27

  • Closed date

    2020-10-30

  • Last modified date

    2021-01-04

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

    IT15770

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

    UI72349

Modules/Macros

  • CMQXKTPU
    

Fix information

  • Fixed component name

    IBM MQ Z/OS V9

  • Fixed component ID

    5655MQ900

Applicable component levels

  • R000 PSY UI72349

       UP20/12/07 P F012 ¢

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.

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Document Information

Modified date:
27 March 2021