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DB2 - Problem description

Problem IC71507 Status: Closed

ENHANCE QUERY PERFORMANCE THROUGH PUSHDOWN OF ANTI-JOIN(S) THROUGH UNION
ALL VIEW(S)

product:
DB2 FOR LUW / DB2FORLUW / 950 - DB2
Problem description:
DB2 Query ReWrite may be able to improve the performance of a 
query by optimizing it during compilation if it satisfies the 
following conditions: 
- The query refers to 2 or more UNION ALL views (UAV) 
- Each UAV branch or operand is one of the following: 
(a) a select over a base table 
(b) an anti-join between 2 base tables (using a not-exists 
subquery) 
(c) an inner, left or right outer join of any combination of (a) 
or (b) 
(d) an inner, left or right outer join of any combination of 
(a), (b) or (c) 
- The UAVs are joined to each other 
- The joins between the UAVs are either all inner joins or joins 
on columns that source from row-preserving sides of any outer 
joins 
 
This enhancement is only available under registry variable 
control. To enable it, issue: 
db2set 
DB2_UNION_OPTIMIZATION=[<other-values>,] 
ENABLE_NESQ_PD_THRU_UA=YES 
[,<other-values>] 
 
and restart the database manager for settings to take effect.
Problem Summary:
**************************************************************** 
* USERS AFFECTED:                                              * 
* ALL                                                          * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* DB2 Query ReWrite may be able to improve the performance of  * 
* a                                                            * 
* query by optimizing it during compilation if it satisfies    * 
* the                                                          * 
* following conditions:                                        * 
*                                                              * 
* - The query refers to 2 or more UNION ALL views (UAV)        * 
*                                                              * 
* - Each UAV branch or operand is one of the following:        * 
*                                                              * 
* (a) a select over a base table                               * 
*                                                              * 
* (b) an anti-join between 2 base tables (using a not-exists   * 
*                                                              * 
* subquery)                                                    * 
*                                                              * 
* (c) an inner, left or right outer join of any combination of * 
* (a)                                                          * 
* or (b)                                                       * 
*                                                              * 
* (d) an inner, left or right outer join of any combination of * 
*                                                              * 
* (a), (b) or (c)                                              * 
*                                                              * 
* - The UAVs are joined to each other                          * 
*                                                              * 
* - The joins between the UAVs are either all inner joins or   * 
* joins                                                        * 
* on columns that source from row-preserving sides of any      * 
* outer                                                        * 
* joins                                                        * 
*                                                              * 
*                                                              * 
*                                                              * 
* This enhancement is only available under registry variable   * 
*                                                              * 
* control. To enable it, issue:                                * 
*                                                              * 
* db2set                                                       * 
*                                                              * 
* DB2_UNION_OPTIMIZATION=[<other-values>,]ENABLE_NESQ_PD_THRU_ * 
* UA                                                           * 
* ES[,<other-values>]                                          * 
*                                                              * 
*                                                              * 
*                                                              * 
* and restart the database manager for settings to take        * 
* effect.                                                      * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 Version 9.5 Fix Pack 8 or later.              * 
****************************************************************
Local Fix:
Manually rewrite any applicable queries to be of the form 
derived through this enhancement.
available fix packs:
DB2 Version 9.5 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 10 for Linux, UNIX, and Windows

Solution
First addressed in DB2 Version 9.5 Fix Pack 8.
Workaround
not known / see Local fix
BUG-Tracking
forerunner  : APAR is sysrouted TO one or more of the following: IC76000 
follow-up : 
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
27.09.2010
31.01.2012
31.01.2012
Problem solved at the following versions (IBM BugInfos)
9.5.FP8
Problem solved according to the fixlist(s) of the following version(s)
9.5.0.8 FixList
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