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IJ01118: DYNAMIC UPDATE TO MON_HEAP_SZ MULTIPLIES THE MEMORY POOL SIZE ADJUSTMENT BY ADDITIONAL 4K

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APAR status

  • Closed as program error.

Error description

  • When performing a dynamic configuration update to the
    MON_HEAP_SZ parameter, the configured memory pool size (visible
    in db2pd -mempools) is set to high - by a factor of 4096.  This
    is due to a logic error where the input size (in 4K page size
    unit) is multipled by 4K twice.
    
    The MON_HEAP_SZ setting in the database configuration will
    appear correct.  The impact is only on the configured size of
    the associated memory pool until the instance is stopped and
    started, at which time the monitor heap memory pool size will be
    freshly and correctly calculated.
    
    The symptoms can vary :
    - no effect (upper limit may be raised with no external symptom)
    - update may fail if the incorrect large size cannot be
    accommodated under an instance memory limit.
    - OOM may occur in other areas if the monitor heap size update
    is successful, as there will be less instance memory available
    than should be the case.  For the same reason, STMM may tune
    down the configuration of a database if STMM is enabled.
    
    For example :
    db2 attach to <instance>  ( so the update is dynamic)
    db2 update dbm cfg using mon_heap_sz 512  (2MB)
    
    We expect the memory pool configuration to be 2MB, instead it is
    * 4096 = 8GB :
    db2pd -mempools output :
    Memory Pools and their subpools:
    PoolName PhySz       PhyHWM    CfgSize       CfgParm
    monh      195428352 644939776 8589934592 MON_HEAP_SZ
    

Local fix

  • avoid dynamic updates to mon_heap_sz
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * ALL                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Db2 11.1 Mod 4 Fixpack 5 or higher                *
    ****************************************************************
    

Problem conclusion

  • First fixed in Db2 11.1 Mod 4 Fixpack 5
    

Temporary fix

Comments

APAR Information

  • APAR number

    IJ01118

  • Reported component name

    DB2 COLUMN STOR

  • Reported component ID

    DB2CLMSTR

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2017-10-30

  • Closed date

    2022-07-03

  • Last modified date

    2022-07-03

  • 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

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

[{"Line of Business":{"code":"LOB10","label":"Data and AI"},"Business Unit":{"code":"BU058","label":"IBM Infrastructure w\/TPS"},"Product":{"code":"SSEPGG","label":"DB2 for Linux- UNIX and Windows"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1"}]

Document Information

Modified date:
04 July 2022