IC78431: DB2 OPTIMIZER CAN CHOOSE A SUB-OPTIMAL PLAN FOR A TABLE THAT HAS A HIGH ROWS-PER-PAGE NUMBER

DB2 Version 9.7 Fix Pack 6 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 7 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 10 for Linux, UNIX, and Windows

APAR status

• Closed as program error.

Error description

• When a table has a high rows-per-page number, DB2 optimizer can
  be too conservative with the estimate and as a result,
  prefetching may not occur for a IXSCAN-FETCH operation on such a
  table, even when the index has a high cluster ratio. This can
  result in a sub-optimal query plan.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users.                                                   *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * See Error Description                                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Upgrade to version 9.7 Fix Pack 6 or later.                  *
  ****************************************************************
  

Problem conclusion

• Problem was first fixed in Version 9.7 Fix Pack 6.
  
  The fix is not enabled by default. To enable it, set the
  following registry:
  
  DB2_EXTENDED_OPTIMIZATION=PG_CR
  

Temporary fix

Comments

APAR Information

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

  IC78403

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

  IC98878

Fix information

• Fixed component name

  DB2 FOR LUW

• Fixed component ID

  DB2FORLUW

Applicable component levels

• R910 PSN

     UP

• R950 PSN

     UP

• R970 PSN

     UP

• R980 PSN

     UP