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LI73150: PERFORMANCE IMPACT FROM NOT ROUTING A QUERY AGAINST A UNION ALL VIEW TO A MQT

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APAR status

  • Closed as program error.

Error description

  • A query referencing a UNION ALL view is not routed to a MQT
    by DB2 since the number of branches of the MQT varies from the
    number of branches in the UNION ALL view.
    This can happen if the original query against the UNION ALL
    view undergoes branch elimination through the predicates
    specified in the query. Branch elimination can result in the
    query having less branches than the original UNION ALL view.
    At this point, the MQT definition is on the original UNION ALL
    view and this results in the MQT definition not matching the
    current Optimized Statement which has undergone branch
    elimination.
    

Local fix

  • Create a MQT that spans the same number of branches seen in
    the Optimized Statement of the query. For example, if the
    original query results in branch elimination that reduces a
    UNION ALL view of 5 branches to 2 branches.  Create a MQT on
    the 2 branches.
    

Problem summary

  • USERS AFFECTED:ALL
    PROBLEM DESCRIPTION:
    A query referencing a UNION ALL view is not routed to a MQT
    by DB2 since the number of branches of the MQT varies from the
    number of branches in the UNION ALL view.
    This can happen if the original query against the UNION ALL
    view undergoes branch elimination through the predicates
    specified in the query. Branch elimination can result in the
    query having less branches than the original UNION ALL view.
    At this point, the MQT definition is on the original UNION ALL
    view and this results in the MQT definition not matching the
    current Optimized Statement which has undergone branch
    elimination.
    
    PROBLEM SUMMARY:
    Gathering the db2exfmt output for the query in question and
    the db2look output should reveal the presence of a UNION ALL
    View and branch elimination occuring.
    
    For more details on branch elimination read the following
    article:
    http://www.ibm.com/developerworks/db2/library/techarticle/0202zu
    zarte/0202zuzarte.pdf
    

Problem conclusion

  • First fixed in Version 9.5, FixPak 1
    

Temporary fix

Comments

APAR Information

  • APAR number

    LI73150

  • Reported component name

    DB2 UDE ESE LIN

  • Reported component ID

    5765F4104

  • Reported release

    950

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    NoHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2008-02-08

  • Closed date

    2009-10-01

  • Last modified date

    2009-10-01

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

    LI72105

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

Modules/Macros

  • ENG_SQNR
    

Fix information

  • Fixed component name

    DB2 UDE ESE LIN

  • Fixed component ID

    5765F4104

Applicable component levels

  • R810 PSN

       UP

  • R820 PSN

       UP

  • R910 PSN

       UP

  • R950 PSN

       UP

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Document Information

Modified date:
01 October 2009