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IT12103: IBM MQ 8.0 A LARGE NUMBER OF GHOST QUEUES GET CREATED WHEN STATQ IS ENABLED.

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APAR status

  • Closed as program error.

Error description

  • When using IBM MQ V8 and queue statistics (STATQ) are enabled
    for dynamic queues, a
    large number of ghost queues get created. In the filesystem
    under the queue manager directory 'queues' more than thousand
    ghost queues like the following may appear:
    
    !!GHOST!4269DF61!0!1A11DF21!13608
    

Local fix

  • Disable STATQ for dynamic queues (via the associated model
    queues).
    

Problem summary

  • ****************************************************************
    USERS AFFECTED:
    This issue affects MQ V8 customers with STATQ resolving to ON
    for a model queue, and therefore for the associated dynamic
    queues. Customers not using dynamic queues are not affected.
    The issue leads to a much larger pool of ghost queues, and
    therefore more file system objects being associated with a queue
    manager.
    It's not a true leak as such as the working set of ghost queues
    will stabalize. There will be a lower rate of reusing of ghost
    queues (to instantiate dynamic queues), but as the performance
    of creating dynamic queues is so much better in MQ V8 this may
    not have a noticeable effect on performance.
    
    
    Platforms affected:
    AIX, HP-UX Itanium, IBM iSeries, Linux on Power, Linux on S390,
    Linux on x86, Linux on x86-64, Linux on zSeries, Solaris SPARC,
    Solaris x86-64, Windows
    
    ****************************************************************
    PROBLEM DESCRIPTION:
    When a dynamic queue is first created, a 'ghost' queue file is
    allocated an initialized to store the attributes and data
    associated with that dynamic queue. When the dynamic queue is
    deleted the 'ghost' queue file is not deleted, but added to a
    cache of such queues associated with the relevant model queue.
    When a dynamic queue is next created based upon that model then
    rather than re-allocating and initializing a new queue file, the
    pre-existing 'ghost' queue file is used to instantiate the new
    dynamic queue.
    
    A previously used dynamic 'ghost' queue cannot be reused until
    all references to the previously used instance of the dynamic
    queue have been released. A typical example of such a reference
    would be is some application had a handle (hObj) open on the
    dynamic queue. There are also a range of possible internal
    references to the dynamic queue, and one of these is related to
    the inheritance of STATQ from the associated model queue.
    
    The reference caused by an effective STATQ of ON was being
    released at the end of each statistics internal, rather than
    when all open handles (hObj's) had been closed (MQCLOSE). The
    effect of this unintended change in V8 was that each ghost queue
    could only be used once in each statistics interval, leading to
    a very large pool of ghost queues being required to effect any
    reuse of these objects.
    

Problem conclusion

  • The queue manager logic has been updated so that the ghost queue
    is available for reuse once all open handles have been closed,
    regardless of the effective value of STATQ.
    
    ---------------------------------------------------------------
    The fix is targeted for delivery in the following PTFs:
    
    Version    Maintenance Level
    v8.0       8.0.0.5
    
    The latest available maintenance can be obtained from
    'WebSphere MQ Recommended Fixes'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
    
    If the maintenance level is not yet available information on
    its planned availability can be found in 'WebSphere MQ
    Planned Maintenance Release Dates'
    http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
    ---------------------------------------------------------------
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT12103

  • Reported component name

    WMQ BASE MULTIP

  • Reported component ID

    5724H7251

  • Reported release

    800

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2015-11-10

  • Closed date

    2015-11-20

  • Last modified date

    2016-07-30

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

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

Fix information

  • Fixed component name

    WMQ BASE MULTIP

  • Fixed component ID

    5724H7251

Applicable component levels

  • R800 PSY

       UP

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Document Information

Modified date:
30 July 2016