IC81066: WITH FILE SYSTEM CACHING ENABLED, SYSTEM OUTAGE MIGHT RESULT IN CORRUPTION DURING LOB OR REORG PROCESSING

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • With file system caching enabled, IBM DB2 for Linux, UNIX and
    Windows uses buffered disk writes for LOB table spaces and
    temporary table spaces used by REORG. Buffered disk writes first
    go to the file system cache and after that when the buffered
    data needs to be physically written to disks, which is typically
    during the commit time, a sync operation must be called.
    
    As a result of an issue in tracking which files needs to be
    synchronized, DB2 mistakenly skips synchronizing some or all of
    the required files. If a machine or file system outage occurs,
    the writes or data that are currently residing in the disk
    buffer and have not yet been written to the disk are lost. The
    time period for which these writes and data are vulnerable is
    dependent on how aggressively the operating system and hardware
    flush file system cache. Under normal conditions, all writes
    will be sent to disks eventually. If an outage happens after the
    writes have been flushed from file system cache to disk, there
    will be no problems. An outage happening before the writes get
    physically written to disks might lead to a potentially large
    variety of symptoms such as:
    
    - LOB data corruption including packed descriptor corruption.
    
    - Reorganization issues when you are copying a reorganized
    object to the table space, or when you are copying the
    reorganized object back to the permanent object. The REORG
    command is only affected when another agent is also sending
    buffered writes to the same table space, and this agent
    synchronizes these writes before the REORG command does. Under
    these conditions, the sync driven by the REORG command is lost.
    
    Note that in this APAR, 'synchronizing' means calling the
    operating system function sync().
    

Local fix

  • - For LOB table spaces: disable file system cache as direct
    writes will be used instead of buffered writes.
    
    - For reorganization process using the REORG command: use a
    dedicated table space for the REORG command, thus ensuring that
    no other agents are doing buffered writes to the same table
    space.
    
    This fix results in an increased number of sync operations. This
    might increase commit latency, especially for transactions
    involving a significant number of buffered writes, for example
    transactions involving a large number of LOB data.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * See APAR Description                                         *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to DB2 for Linux, Unix, and Windows version 9.7 Fix  *
    * Pack 6                                                       *
    ****************************************************************
    

Problem conclusion

  • Problem first fixed in DB2 for Linux, Unix, and Windows version
    9.7 Fix Pack 6
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC81066

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    970

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2012-01-27

  • Closed date

    2012-06-04

  • Last modified date

    2012-06-06

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

    IC81062

  • 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

  • R970 PSY

       UP



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Document information


More support for:

DB2 for Linux, UNIX and Windows

Software version:

9.7

Reference #:

IC81066

Modified date:

2012-06-06

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