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IT21816: The optimizer might choose a non-optimal full table scan compared to a better performing index access on the inner of an NLJOIN

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You can track all active APARs for this component.

 

APAR status

  • Closed as program error.

Error description

  • In some cases, the optimizer might over-estimate the cost of an
    NLJOIN operation, leading to the optimizer favoring a full table
    scan of a table access over an index access scan of that access
    on the inner of a NLJOIN.  Typically, the favored choice will be
    a sub-optimal HSJOIN with the table access on the outer branch.
    

Local fix

  • Ensuring that the statistics are up to date can help alleviate
    this problem.  If not, an optimization guideline can be used to
    request the NLJOIN method.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * ALL                                                          *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Upgrade to Db2 11.1 Mod 3 Fix Pack 3 or higher               *
    ****************************************************************
    

Problem conclusion

  • First fixed in Db2 11.1 Mod 3 Fix Pack 3
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT21816

  • 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

    2017-08-04

  • Closed date

    2018-03-19

  • Last modified date

    2018-03-19

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

    IT13898

  • 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

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Document Information

Modified date:
19 March 2018