|
Problem IC73877
|
Status: Closed |
THE OPTIMIZER MAY CHOOSE A SUB-OPTIMAL ACCESS PLAN FOR SQL USING SUB-SELECT & PLACE HOLDER VARIABLE. |
| product: |
DB2 FOR LUW / DB2FORLUW / 950 - DB2 |
| Problem description: |
The optimizer may choose a sub-optimal access plan for an SQL
statement which uses an IN and a place holder variable as part
of the FROM clause.
e.g.
select ... from tab1, tab2 where tab1.COLA=tab2.COLA and
tab1.COLB IN (?,?,?,...);
If there is an index with t1.COLB as the leading column in the
key, the optimizer can consider an in-to-join transformation of
the IN predicate shown in the WHERE clause.
If the access of tab1 is on the inner of a NLJN, the optimizer
might consider a plan with a TEMP over the inner access that
might be beneficial for the in-to-join access on the inner. In
general, this is a good option to consider but when there are
statement place holders, the cardinality estimates cannot always
be accurate. |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* All Platforms *
****************************************************************
* PROBLEM DESCRIPTION: *
* THE OPTIMIZER MAY CHOOSE A SUB-OPTIMAL ACCESS PLAN FOR SQL *
* USING *
* SUB-SELECT & PLACE HOLDER VARIABLE. *
****************************************************************
* RECOMMENDATION: *
* Upgrade to v9.5FP8 or higher *
**************************************************************** |
| Local Fix: |
dbset DB2_EXTENDED_IN2JOIN=NLJN_TEMP_OFF |
| 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 fixed in v9.5FP8 or higher |
| Workaround |
not known / see Local fix |
| BUG-Tracking |
forerunner : APAR is sysrouted TO one or more of the following: IC73907
follow-up : |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 14.01.2011
07.07.2011
07.07.2011 |
| 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
|
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