IBM Support

IT38686: Db2 write performance on Linux might be affected due to file system journal waits

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APAR status

  • Closed as program error.

Error description

  • For 11.1 release only PowerPC platform is affected.
    Regression could be noticed when one upgrades from 10.5 or
    older.
    
    On Linux, Db2 uses O_SYNC flag (04000000) to open
    database containers, which enforces more strict file system
    synchronisation requirements during writes than O_DSYNC
    (00010000) flag used with releases 11.1 and older.
    This might result in a performance degradation for workloads
    that depend heavily on synchronous writes (e.g. on systems with
    small bufferpools). The impact might vary for different file
    systems and file system cache configuration for given
    tablespace, with the system managed tablespaces (SMS) that use
    file caching being affected the most.
    For Db2's data consistency O_DSYNC is sufficient and this APAR
    will address this regression.
    
    Symptoms will include
    - increased synchronous write time in Db2 monitoring interfaces
    - Db2 threads blocked longer in the IO code path, waiting on
    file system journal (e.g. as indicated by jbd2_log_wait_commit
    WCHAN in "ps -T" output for Db2 engine/db2sysc).
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * N/A                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Db2 v11.5.5.1 or request a special build          *
    ****************************************************************
    

Problem conclusion

  • N/A
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT38686

  • 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

    2021-10-12

  • Closed date

    2021-10-12

  • Last modified date

    2021-10-13

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

    IT35880

  • 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":"BU053","label":"Cloud \u0026 Data Platform"},"Product":{"code":"SSEPGG","label":"DB2 for Linux- UNIX and Windows"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1"}]

Document Information

Modified date:
14 October 2021