IBM Support

IC78431: DB2 OPTIMIZER CAN CHOOSE A SUB-OPTIMAL PLAN FOR A TABLE THAT HAS A HIGH ROWS-PER-PAGE NUMBER

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You can track all active APARs for this component.

APAR status

  • Closed as program error.

Error description

  • When a table has a high rows-per-page number, DB2 optimizer can
    be too conservative with the estimate and as a result,
    prefetching may not occur for a IXSCAN-FETCH operation on such a
    table, even when the index has a high cluster ratio. This can
    result in a sub-optimal query plan.
    

Local fix

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * All users.                                                   *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to version 9.7 Fix Pack 6 or later.                  *
    ****************************************************************
    

Problem conclusion

  • Problem was first fixed in Version 9.7 Fix Pack 6.
    
    The fix is not enabled by default. To enable it, set the
    following registry:
    
    DB2_EXTENDED_OPTIMIZATION=PG_CR
    

Temporary fix

Comments

APAR Information

  • APAR number

    IC78431

  • 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

    2011-08-31

  • Closed date

    2012-06-05

  • Last modified date

    2014-01-28

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

    IC78403

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

    IC98878

Fix information

  • Fixed component name

    DB2 FOR LUW

  • Fixed component ID

    DB2FORLUW

Applicable component levels

  • R910 PSN

       UP

  • R950 PSN

       UP

  • R970 PSN

       UP

  • R980 PSN

       UP



Document information

More support for: DB2 for Linux, UNIX and Windows

Software version: 9.7

Reference #: IC78431

Modified date: 28 January 2014