|
Problem IC78742
|
Status: Closed |
INACCURATE COLCARD STATISTICS UNDER RARE CONDITIONS WHICH CAN LEAD TO POOR PERFORMANCE. |
| product: |
DB2 FOR LUW / DB2FORLUW / 970 - DB2 |
| Problem description: |
Under rare conditions, the COLCARD statistics value of a column
might be significantly inaccurate. Inaccurate statistics might
lead the query optimizer to determine a poor performing access
plan.
When a column is the leading column of an index, the index can
be used to provide an accurate colcard. When no such index is
available, DB2 will estimate the colcard, and this is the
situation where the problem may be observed.
When the problem is observed, the inaccurate colcard determined
will be 254 when TABLESAMPLE option is not used, and 1022 when
the TABLESAMPLE option is used.
If you suspect you are experiencing the problem, you can compare
the colcard with the actual unique count for the column. It is
normal for the two to be different. If the colcard estimate is
highly inaccurate, and its value is either 254 or 1022, then you
are possibly experiencing the problem. |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* All users on DB2 v97 FP5 and earlier *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 9.7 FP6 or subsequent fix pack. *
**************************************************************** |
| Local Fix: |
As a workaround, if possible, create an index where the column
is the leading column of the index, and then perform a table and
index statistics collection using the AND INDEXES clause. |
| available fix packs: |
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
|
| Solution |
First Fixed in DB2 Version 9.7 Fix Pack 6 |
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 16.09.2011
22.06.2012
29.01.2013 |
| Problem solved at the following versions (IBM BugInfos) |
9.7.FP6
|
| Problem solved according to the fixlist(s) of the following version(s) |
| 9.7.0.6
|
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