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MF60904 - LIC-DB-OTHER-PERFM Improved column statistics collection for

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Abstract

LIC-DB-OTHER-PERFM Improved column statistics collection for


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
CO   5770999  V7R2M0    MF60905   00/00    0000



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APAR Error Description / Circumvention

-----------------------------------------------
In order to provide fast running SQL query plans, the statistics
engine periodically gathers and refreshes column statistics for
a table. These refreshes occur when the statistics engine
determines that the data in the table has changed sufficiently
from the last statistic collection. The statistics engine uses
the same time-based and change-based metric for all tables.
However, SQL provides the VOLATILE attribute to indicate to the
query optimizer that the number of rows in a table may be
changing frequently. This attribute does not influence the
collection of column statistics.

CORRECTION FOR APAR MA45078 :
-----------------------------
This fix allows the statistics engine to consider the VOLATILE
attribute of the table being optimized. A table that is VOLATILE
will refresh its column statistics after a number of changes
that is much lower than for a NOT VOLATILE table. As a result,
the column statistics on a VOLATILE table will be more
responsive to changes to both the table size and table data.
Users who find that the optimizer does not re-optimize query
plans sufficiently for tables with frequent changes should
consider marking the table VOLATILE after applying this fix.
This should be done carefully, as making a table VOLATILE may
lead to increased resource usage due to more frequent column
statistic collection and query re-optimization.

CIRCUMVENTION FOR APAR MA45078 :
--------------------------------
None.


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Supersedes

PTF/FIX NO(S).  APAR TITLE LINE
--------------  ------------------------------------------------------------
     NONE

Summary Information

System..............................i
Models..............................
Release.............................V7R2M0
Licensed Program...............5770999
APAR Fixed..........................View details for APAR MA45078
Superseded by:......................
Recompile...........................N
Library.............................QSYS
MRI Feature ........................NONE
Cum Level...........................C6127720


System i Support

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Document Information

Modified date:
26 January 2016