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Problem IC97414
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Status: Closed |
SYSCAT.COLUMNS.NUMNULLS STATISTICS MIGHT BE INACCURATE AT ALL TABLE SAMPLING RATES. |
| product: |
DB2 FOR LUW / DB2FORLUW / A50 - DB2 |
| Problem description: |
Problem description
When RUNSTATS is executed with the TABLESAMPLE option, the
NUMNULLS statistics might be inaccurate for columns that do not
appear as a leading column in an index. The problem is
encountered under some circumstances which is dependent on the
distribution of NULL and non-NULL values of the column in the
table. When the problem occurs, you will likely observe that
increasing the sampling rate does not help to improve the
accuracy.
This problem was first introduced in DB2 V10.1. |
| Problem Summary: |
****************************************************************
* USERS AFFECTED: *
* ALL *
****************************************************************
* PROBLEM DESCRIPTION: *
* See Error Description *
****************************************************************
* RECOMMENDATION: *
* Upgrade to DB2 version v10.5 Fix pack 4 *
**************************************************************** |
| Local Fix: |
Workarounds for this problem are:
- Execute runstats without the TABLESAMPLE option.
- Create an index with the column as the lead column, and
collect table and index statistics for the table; if the column
is extensively used in predicates, such an index will also be
beneficial for query performance.
- Manually update SYSSTAT.COLUMNS.NUMNULLS with a more accurate
value; if AUTO_RUNSTATS is enabled, the table is excluded from
automatic statistics collection until you execute a RUNSTATS on
the table, which serves to indicate to DB2 that the manual
update is no longer needed. |
| available fix packs: |
DB2 Version 10.5 Fix Pack 3 for Linux, UNIX, and Windows
DB2 Version 10.5 Fix Pack 3a for Linux, UNIX, and Windows
DB2 Cancun Release 10.5.0.4 (also known as Fix Pack 4) for Linux, UNIX, and Windows
DB2 Version 10.5 Fix Pack 9 for Linux, UNIX, and Windows
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| Solution |
|
| Workaround |
not known / see Local fix |
| Timestamps |
Date - problem reported :
Date - problem closed :
Date - last modified :
| 05.11.2013
02.04.2014
02.04.2014 |
| Problem solved at the following versions (IBM BugInfos) |
|
| Problem solved according to the fixlist(s) of the following version(s) |
| 10.5.0.3
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| 10.5.0.3
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