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IC77857: STMM OVERCOMMITS MEMORY ON LINUX

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • STMM does not make sufficient allowance for system memory
    requirements in two cases:
    - memory which is paged out and only exists in paging space is
    not accounted for, which can result in continually increasing
    tunings if Linux is swapping out memory before DB2 perceives a
    system to be overcommitted
    - large file cache requirements due to a high amount of dirty
    pages.  Dirty file pages cannot be reclaimed until they are
    laundered (written out), and contribute to the level of
    committed memory on a system.  A high volume of dirty pages may
    be triggered by activity on tablespaces with buffered I/O (such
    as sort, reorgs in SMS temporary tablespaces where buffered I/O
    is the default), backups to disk, other.
    
    The lack of accounting for these two cases may contribute to
    swapping on the system.  Note that vm.swappiness should be set
    to 0 on all DB2 system, otherwise swapping may occur on systems
    which are not overcommitted (memory requirements are not
    exceeding RAM).
    

Local fix

  • Use DB2_BACKUP_USE_DIO for backups to disk, non-buffered DMS
    temporary tablespaces instead of SMS.
    Ensure vm.swappiness is set to 0.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * DB2/Linux systems with self-tuning of Database Memory        *
    * enabled (SELF_TUNING_MEM=ON, DATABASE_MEMORY=AUTOMATIC)      *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to DB2 Version 9.7 Fix Pack 5                        *
    ****************************************************************
    

Problem conclusion

  • Problem first fixed in DB2 Version 9.7 Fix Pack 5
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC77857

  • 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

    2011-07-31

  • Closed date

    2012-03-29

  • Last modified date

    2012-03-29

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

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

Modules/Macros

  • sqo
    

Fix information

  • Fixed component name

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

  • R970 PSN

       UP



Document information

More support for: DB2 for Linux, UNIX and Windows

Software version: 9.7

Reference #: IC77857

Modified date: 29 March 2012