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MF67345 - OSP-OTHER-PERFM QUERY INTERMITTENTLY PERFORMS POORLY WHEN CO

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Abstract

OSP-OTHER-PERFM QUERY INTERMITTENTLY PERFORMS POORLY WHEN CO


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
CO   5770999  V7R2M0    MF67344   00/00    0000



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-------
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APAR Error Description / Circumvention

-----------------------------------------------
A query, over a file that contains a date column that is rapidly
changing, performs poorly when the optimizer obtains statistics
from a column stat versus an index. The column stat is not
marked stale but its values are not current enough to provide a
good record count estimate for the date predicates thus,
occasionally leading to a low estimate and a poor performing
access plan.

Example:
SELECT * FROM FILE WHERE A.DATECOLUMN >= ? and A.DATECOLUMN <= ?

CORRECTION FOR APAR MA48360 :
-----------------------------
If the predicates include a range completely outside of the
range represented by the column stats, the stats engine will use
an index to verify record count estimates. This should improve
the accuracy of the estimate. Previously, the estimation
algorithm would make assumptions about the rows not represented
by the column stats, which led to poor estimates in some cases.

CIRCUMVENTION FOR APAR MA48360 :
--------------------------------
None.


Activation Instructions


None.




Special Instructions


None.


Default Instructions

THIS PTF CAN BE APPLIED IMMEDIATE OR DELAYED.



Supersedes

PTF/FIX NO(S).  APAR TITLE LINE
--------------  ------------------------------------------------------------
   MF65897      OSP-DB-OTHER-F/STRINGHIGHUSE-T/QQQOOODBOP-MSGMCH3402 A MSGMH
   MF64903      OSP-OTHER-PERFM JOIN QUERY PERFORMANCE
   MF64875      OSP-PERFM JOIN ORDER NOT CHOSEN WELL AT 7.2
   MF63097      OSP-OTHER-PERFM QUERY PERFORMING POORLY DUE TO INCORRECT EST
   MF60825      OSP-DB-OTHER-PERFM NO OR INCORRECT INDEX USED WHEN LARGE IN
   MF59413      OSP-DB-OTHER-UNPRED MSGMCH3203 VL0600A029 VL02001720

Summary Information

System..............................i
Models..............................
Release.............................V7R2M0
Licensed Program...............5770999
APAR Fixed..........................View details for APAR MA48360
Superseded by:......................
Recompile...........................N
Library.............................QSYS
MRI Feature ........................NONE
Cum Level...........................C1084720


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Document Information

Modified date:
17 April 2021