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IT17489: SELECT AGAINST AN MDC TABLE WITH A RANGE PREDICATE IN SMP MIGHT RETURN A WRONG RESULT

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APAR status

  • Closed as program error.

Error description

  • In a rare timing scenario SQL doing a range table scan on a MDC
    table in SMP mode only could loose rows from the result set.
    
    There are optimizations in DB2 to determine the best next range
    for each subagent to scan based on the usage of the system.
    However, the calculation in the optimization does not ensure
    each scan range is within the MDC block boundary and end up with
    a range covering more than a single block.  On the other hand,
    block predicate evaluation on a MDC table scan is done only once
    per range since it does not expect the scan range to cross a
    block boundary, it can incorrectly skip pages that would have
    been qualified for the scan predicate.  And this is timing
    related.
    

Local fix

  • Disable SMP mode.
    Or don't specify a range predicate on the MDC columns.
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED:                                              *
    * MDC Tables                                                   *
    ****************************************************************
    * PROBLEM DESCRIPTION:                                         *
    * See Error Description                                        *
    ****************************************************************
    * RECOMMENDATION:                                              *
    * Please, apply this fix.                                      *
    ****************************************************************
    

Problem conclusion

  • Please, apply this fix.
    

Temporary fix

Comments

APAR Information

  • APAR number

    IT17489

  • Reported component name

    DB2 FOR LUW

  • Reported component ID

    DB2FORLUW

  • Reported release

    B10

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt / Xsystem

  • Submitted date

    2016-10-13

  • Closed date

    2017-10-10

  • Last modified date

    2017-10-10

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

    IT17395

  • 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

[{"Business Unit":{"code":"BU053","label":"Cloud & Data Platform"},"Product":{"code":"SSEPGG","label":"Db2 for Linux, UNIX and Windows"},"Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"11.1","Line of Business":{"code":"LOB10","label":"Data and AI"}}]

Document Information

Modified date:
29 June 2020