DB2 FOR LUW / DB2FORLUW / 970 - DB2

This only applies to a DPF environment.  For queries involving 
joins of non-collocated tables, the query optimizer may favour 
repartitioning one stream over broadcasting the other to perform 
the join.  If the join column that the stream is partitioned on 
is highly skewed, the broadcast alternative may be a better 
choice. This apar will improve the optimizer's model of skew in 
a DPF environment.  This is more likely to impact systems with 
hundreds of database partitions. 
You may be experiencing this issue if one database partition is 
performing a significant larger amount of work than other 
partitions.

**************************************************************** 
* USERS AFFECTED:                                              * 
* Problem is specific to DPF environment                       * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* For queries involving joins of non-collocated tables,        * 
* thequery optimizermight favour repartitioning one stream     * 
* over broadcasting theother toperform the join.  If the join  * 
* column that the stream ispartitioned onis highly skewed, the * 
* broadcast alternative may be a betterchoice. This apar will  * 
* improve the optimizer's model of skewina DPF environment.    * 
* This is more likely to impact systemswithhundreds of         * 
* database partitions.You may be experiencing this issue if    * 
* one database partitionisperforming a significant larger      * 
* amount of work than otherpartitions.                         * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 9.7 Fix Pack 4 and set                * 
* the DB2_EXTENDED_OPTIMIZATION registry variable to           * 
* db2set DB2_EXTENDED_OPTIMIZATION=DPFCOST_SKEW                * 
* Note: if you already have DB2_EXTENDED_OPTIMIZATION          * 
* set, then you will need to include it when setting this new  * 
* keyword; for example,                                        * 
* DB2_EXTENDED_OPTIMIZATION=YES,DPFCOST_SKEW                   * 
****************************************************************

1.  The optimizer relies on non-uniform distribution statistics 
to model the skew.  If distribution statistics are not collected 
on the join column(s), the first step required in resolving this 
issue is to ensure distribution statistics are collected. 
2.  If distribution statistics are collected and the problem 
persists, replicated tables can be created to eliminate the need 
to repartition the data stream.

DB2 Version 9.7 Fix Pack 4 for Linux, UNIX, and Windows
 DB2 Version 9.7 Fix Pack 5 for Linux, UNIX, and Windows
 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
 

Problem was first fixed in Version 9.7 Fix Pack 4

See LOCAL_FIX

Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :

10.09.2010
19.05.2011
19.05.2011

9.7.FP4