PM27249: RUNSTATS HISTOGRAM PRODUCES UNEVENLY DISTRIBUTED QUANTILES

A fix is available

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APAR status

  • Closed as program error.

Error description

  • Runstats histogram produces unevenly distributed quantiles, with
    a lot of data fall into the last quantile
    

Local fix

  • N/A
    

Problem summary

  • ****************************************************************
    * USERS AFFECTED: All DB2 9 for z/OS and all DB2 10 for        *
    *                 z/OS users of RUNSTATS utility collecting    *
    *                 HISTOGRAM statistics.                        *
    ****************************************************************
    * PROBLEM DESCRIPTION: MSGDSNU636I and MSGDSNU632I shows       *
    *                      uneven distribution in quantiles        *
    *                      during RUNSTATS collection of           *
    *                      HISTOGRAM statistics.                   *
    ****************************************************************
    * RECOMMENDATION: Apply corrective PTF when available          *
    ****************************************************************
    When the user executed RUNSTATS INDEX or RUNSTATS TABLESPACE
    utility to collect HISTOGRAM statistics, MSGDSNU636I and
    MSGDSNU632I showed uneven distribution in quantiles. These
    statistics were stored in SYSIBM.SYSCOLDISTSTATS and
    SYSIBM.SYCOLDIST catalog tables.
    
    The uneven distribution in quantiles were caused by
    1. An incorrect estimation of the table cardinality.
    2. The algorithm to determine when to cut the quantile
    did not optimally cut the quantiles in the case of skewed data.
    

Problem conclusion

  • The code was modified to produce more even distribution in
    in the quantiles as follows:
    
    1. To better estimate the number of records in the index
    during RUNSTATS INDEX execution.
    
    2. The algorithm to collect HISTOGRAM statistics was changed
    to be more adaptive on skewed data distribution.
    
    3. The HISTOGRAM statistics will collect HIGH values and LOW
    values in separate dedicated quantiles.
    

Temporary fix

Comments

APAR Information

  • APAR number

    PM27249

  • Reported component name

    DB2 OS/390 & Z/

  • Reported component ID

    5740XYR00

  • Reported release

    910

  • Status

    CLOSED PER

  • PE

    NoPE

  • HIPER

    YesHIPER

  • Special Attention

    NoSpecatt

  • Submitted date

    2010-11-22

  • Closed date

    2011-05-17

  • Last modified date

    2011-07-05

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

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

    UK67816 UK67817

Modules/Macros

  •    DSNUSAH1 DSNUSAH2 DSNUSDST DSNUSIDX DSNUSIIX
    DSNUSITS
    

Fix information

  • Fixed component name

    DB2 OS/390 & Z/

  • Fixed component ID

    5740XYR00

Applicable component levels

  • RA10 PSY UK67816

       UP11/06/02 P F106

  • R910 PSY UK67817

       UP11/06/02 P F106

Fix is available

  • Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.



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Document information


More support for:

DB2 for z/OS

Software version:

910

Reference #:

PM27249

Modified date:

2011-07-05

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