PM00464: DUMP TITLE: ABN=071-00000000,U=SYSOPR,C=L8200.600.BUFF-CSQP3DWP,M=CSQGFRCV,PSW=077C000098C17684,ASID=0000

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APAR status

  • Closed as program error.

Error description

  • Dump Title: ABN=071-00000000,U=SYSOPR,C=L8200.600.BUFF-CSQP3DWP,
    M=CSQGFRCV,PSW=077C000098C17684,ASID=0000
    .
    A spin loop occurs because CSQP2DWP repeatedly calls CSQP3DWP
    to (unsuccessfully) clear buffers of the Deferred Write Queue.
    The most likely likely reason that CSQP3DWP cannot free any
    buffers is that all of the buffers on the DWQ are clean (this is
    the case in the dump), and CSQP3DWP is unable to get the lru
    latch and so is unable to process any of them.
    The lru latch is held briefly by CSQP1REL (which is being called
    as part of the pageset expansion that is taking place on the
    same pageset), however it is possible that this task could be
    interrupted while holding the latch. If this occurs the dwp will
    loop until the task is redispatched and releases the latch.
    However, the deferred write process runs as an srb, and does not
    give up control of the cpu while looping; in a busy system this
    can mean that the task holding the latch does not get a chance
    to run, and so cannot release the latch.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All users of WebSphere MQ for z/OS Version 6 *
    ****************************************************************
    * PROBLEM DESCRIPTION: Loop in deferred write processor causes *
    *                      high CPU. Abend 071, followed by qmgr   *
    *                      termination may also result.            *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    During pageset expansion a large number of pages were added to
    the deferred write queue, causing it to rise above the threshold
    value.The deferred write processor was invoked, and CSQP2DWP
    called CSQP3DWP to process the dwq queue. None of the pages
    required any I/O, and so needed moving to the LRU chain for the
    bufferpool. This required the lru chain latch, which was held by
    the pageset expansion task.
    CSQP3DWP returned to CSQP2DWP, however the dwq was still above
    the threshold, and so CSQP3DWP was reinvoked.
    The SRB running CSQP2DWP continues to invoke CSQP3DWP until the
    depth drops below the threshold, which can only occur when the
    latch is unavailable.
    In a busy system the latch holder may not get redispatched in
    a timely manner, especially with the SRB running on one of the
    cpus, leading to the loop continuing.
    

Problem conclusion

  • CSQP2DWP is changed to suspend if unable to process the DWQ,
    relinquishing the cpu to enable the latch holder to run and
    release the latch.
    000Y
    CSQP2DWP
    

Temporary fix

  • *********
    * HIPER *
    *********
    

Comments

  • ž**** PE10/10/29 FIX IN ERROR. SEE APAR PM22696  FOR DESCRIPTION
    

APAR Information

  • APAR number

    PM00464

  • Reported component name

    WMQ Z/OS V6

  • Reported component ID

    5655L8200

  • Reported release

    000

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2009-11-04

  • Closed date

    2010-01-04

  • Last modified date

    2010-11-16

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

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

    PM04109 UK53282

Modules/Macros

  •    CSQP2DWP
    

Fix information

  • Fixed component name

    WMQ Z/OS V6

  • Fixed component ID

    5655L8200

Applicable component levels

  • R000 PSY UK53282

       UP10/02/04 P F002

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


More support for:

WebSphere MQ
APAR

Software version:

6.0

Reference #:

PM00464

Modified date:

2010-11-16

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