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IT20887: POOR PERFORMANCE IN A FEDERATED ENVIRONMENT WHEN LOCAL PREDICATEON COLUMNS WITH SMALL NUMBER OF DISTINCT VALUES, <=3.

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You can track all active APARs for this component.

 

APAR status

  • Closed as program error.

Error description

  • Poor performance may be seen with a federated query due to a
    poor access plan selection due to the lack of statistics for the
    federated data.
    This is due to the  high2key and low2key values not be retrieved
    where the column cardinality (colcard) <=3
    
    This will only be enabled when the following DB2 Registry
    parameter is set:
      DB2_SELECTIVITY=EXTDIST_CC1
    

Local fix

  • Use Optimizer Profile to ensure that a good access plan is used
    for the query.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * All Db2 Federated users                                      *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Db2 11.1.2.2 or later.                            *
    ****************************************************************
    

Problem conclusion

  • First fixed in Db2 11.1.2.2.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT20887

  • 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

    2017-06-06

  • Closed date

    2017-10-10

  • Last modified date

    2017-10-10

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

    IT15854

  • 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

  • RB10 PSN

       UP

  • RB10 PSY

       UP

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Document Information

Modified date:
10 October 2017