|
Problem IC99697
|
Status: Closed |
SUBOPTIMAL PERFORMANCE AS QUERY REWRITE INCORRECTLY DECIDES NOT TO PUSH DOWN AN INNER JOIN |
| product: |
DB2 FOR LUW / DB2FORLUW / 970 - DB2 |
| Problem description: |
The Query Rewrite component of the DB2 Query compiler will
perform a cost based evaluation to see whether pushing down an
inner join into a left outer join
is beneficial for query performance. Due to a problem introduced
by the fix of APAR IC83902, V9.7 Fix Pack 9 may wrongly
calculate this cost and hence make the wrong decision.
This may lead to performance regression of some statements in
V9.7 Fix Pack 9 compared to earlier Fix Pack releases.
You may be able to identify this issue by comparing the
"Optimized Statement" section in the db2exfmt output of a
statement with the same generated on an earlier Fix Pack. |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* All *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 Version 9.7 Fix Pack 10 *
**************************************************************** |
| Local Fix: |
Setting :
db2set DB2COMPOPT=327685,268435456
and restarting the DB2 instance, will disable the fix for APARr
IC83902.
However as it also disables the fix for APAR
http://www-01.ibm.com/support/docview.wss?uid=swg1IC79170
the workaround should be used with caution. |
| Solution |
First fixed in DB2 Version 9.7 Fix Pack 10 |
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 27.02.2014
11.11.2014
11.11.2014 |
| Problem solved at the following versions (IBM BugInfos) |
9.7.FP10
|
| Problem solved according to the fixlist(s) of the following version(s) |
| 9.7.0.10
|
 |
