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PI14696: DSNSCON2 ABEND0C4 CONTRACTING 64BIT VARIABLE POOL OR ABEND04E RC00E20005 AT DSNSVSPP +09D6 OFFSET09D6 14/06/24 PTF PECHANGE

A fix is available

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APAR status

  • Closed as program error.

Error description

  • DSNSCON2 abend0c4 during contraction of an 64bit pool, in this
    case the SQL ARRAY POOL 4G which is a DB2 system level pool.
    .
    This is a PE fixing APAR for PM86952/UK97692 V10
    PM95296/UK98204 V11
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All DB2 V10 and higher                       *
    ****************************************************************
    * PROBLEM DESCRIPTION: Abend0c4 in dsnscon2 while contracting  *
    *                      a system level Above-the-bar pool. In   *
    *                      this case it was the SQL ARRAY POOL 4G  *
    *                      which is a Shared Storage pool but may  *
    *                      occur on any 64bit ATB pool.            *
    ****************************************************************
    * RECOMMENDATION:                                              *
    ****************************************************************
    While contracting an ATB shared storage pool, an abend0c4 occurs
    when DSNSCON2 runs out of forward pointers before the search
    condition has been satisfied. The pool has multiple consecutive
    segments which are eligible for contraction, beginning with the
    anchor segment.  However, just as the pvts blocks are being
    removed from the xslot_segchain, additional pvts have been
    pushed onto the anchor and the Compare and Swap fails.  The
    subsequent logic to find position and dechain the eligible
    segments is incorrect, leaving a contracted segment pvts on the
    chain.  Though the pvts is still chained, the actual segment is
    freed and available for reuse by any thread.  Next time this
    same pool is contracted, it will likely abend0c4.
    This will only fail for 64 bit pools which are shared,
    such as system level pools, since non-shared pools should not
    have expansions while being contracted. However, the segment
    which has been freed may be picked up by ANY thread and result
    in an abend by that thread also. Also, if the DB2 is under
    full system contraction, this failure may occur even for
    non-shared pools since the contraction is done in parallel
    by a system thread. ***NOTE*** If the contracted segment is
    picked up by a thread and used for THIS POOL xslot expansion,
    it may result in an infinite loop and HIGH CPU in DBM1 starting
    with the next contraction of this pool xslot.
    

Problem conclusion

  • Code has been changed to properly dechain eligible segments from
    the pool xslot_segchain.
    

Temporary fix

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

Comments

APAR Information

  • APAR number

    PI14696

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    A10

  • Status

    CLOSED PER

  • PE

    YesPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2014-03-27

  • Closed date

    2014-04-24

  • Last modified date

    2014-09-12

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

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

    UI17409 UI17410

Modules/Macros

  • DSNSCON2
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UI17409

       UP14/05/10 P F405 ½

  • RB10 PSY UI17410

       UP14/05/10 P F405 ½

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:
12 September 2014