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IC82182: A LOGIC ERROR IN STMM"S SORTHEAP RESERVATION TRACKING ARTIFICIALLY INCREASES STMM SORT TUNING

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APAR status

  • Closed as program error.

Error description

  • A logic error in STMM's tracking of throttled sort requests
    results in a continuous upward trend in the enforced minimum
    size for shared sort (SHEAPTHRES_SHR).  This may cause other
    STMM-tuned areas to be forced down, potentially causing
    performance degradation or other resource issues (SQL1218).
    
    This problem exists in:
    Version 9.1 Fix Pack 6 and higher
    Version 9.5 Fix Pack 2 and higher
    Version 9.7 GA and higher
    
    The following entry can be seen in STMM logs each time a
    permanent increase is introduced (at DIAGLEVEL 3 or above)
    
    FUNCTION: DB2 UDB, Self tuning memory manager,
    stmmRegisterReserveSharedSortSpace, probe:3038
    MESSAGE : Unexpected value in accounting of reserved sort memory
    -  91545 -  1
              -  5409 -  10641 -  0
    
    Occasionally STMM may detect that the minimum size has grown
    beyond a reasonable range, and may cap the minimum size, as
    evidenced by the following STMM log entry (logged regardless of
    DIAGLEVEL):
    
    FUNCTION: DB2 UDB, Self tuning memory manager,
    stmmComputeMinSHEAPTHRES, probe:837
    MESSAGE : Unexpected minimum value for SHEAPTHRES_SHR - value
    automatically
              corrected -  299025 -  2076 -  342641 -  249120 -  96
    -  0 -
              96.000000 -  1 -  31 -  274113 -  735
    
    The values are only maintained while the database is active, so
    recycling the database will reset the minimum size to normal
    values.  Alternatively, use a fixed setting for SHEAPTHRES_SHR
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * Systems where STMM is configured to tune SORT memory         *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to DB2 Version 9.7 Fix Pack 7                        *
    ****************************************************************
    

Problem conclusion

  • Problem first fixed in DB2 Version 9.7 Fix Pack 7
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC82182

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    970

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-03-21

  • Closed date

    2012-10-30

  • Last modified date

    2012-10-30

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

    IC82154

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

Modules/Macros

  • stmm
    

Fix information

  • Fixed component name

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

  • R970 PSN

       UP

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Document Information

Modified date:
30 October 2012