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IT21181: SUBOPTIMAL PERFORMANCE MAY PERSIST ON AN STMM-TUNED SYSTEM DUE TO LARGE CONSUMER NOT GIVING UP MEMORY

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You can track all active APARs for this component.

 

APAR status

  • Closed as program error.

Error description

  • On an STMM-tuned system, when there is a very large memory
    consumer that suddenly becomes idle (in very little need of
    memory), and there is no need to reassign that memory to other
    consumers for a lengthy period (>= 2 hours), STMM may
    subsequently not give memory to other needy consumers (eg. when
    workload ramps up).
    
    This occurs because of conflicting heuristics in STMM's tuning
    model.  A consumer for which historical statistics are "weak"
    will release memory in small amounts.  But those calculated
    amounts may be cancelled out when a separate minimum decrease
    size threshold test is applied.
    
    This situation is rare as the stubborn consumer must be very
    large, the demands of the other consumers modest, and, as stated
    above, there must be a fairly specific and extreme pattern in
    memory demands among the STMM-tuned memory consumers.
    

Local fix

  • Dynamically decrease the configuration of the stubborn large
    consumer in 25% decrements, waiting for ~5 minutes between each
    step before determining if tuning has normalized.
    i.e.
      db2 connect to <database>
      db2 alter/update <STMM consumer>... AUTOMATIC
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * larger systems using STMM (self-tuning memory manager)       *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * upgrade to DB2 Version 11.1 Mod 3 Fix Pack 3                 *
    ****************************************************************
    

Problem conclusion

  • Problem first solved in DB2 Version 11.1 Mod 3 Fix Pack 3
    

Temporary fix

  • see Local Fix
    

Comments

APAR Information

  • APAR number

    IT21181

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2017-06-26

  • Closed date

    2018-03-15

  • Last modified date

    2018-03-15

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

    IT20400

  • 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

  • RB10 PSN

       UP

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Document Information

Modified date:
15 March 2018