PM27249: RUNSTATS HISTOGRAM PRODUCES UNEVENLY DISTRIBUTED QUANTILES

Obtain the fix for this APAR.

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 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.