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MF68793 - OSP-OTHER-PERFM INCREASE IN KEY RANGE ESTIMATES

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PTF ( Program Temporary Fixes ) Cover letter


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Abstract

OSP-OTHER-PERFM INCREASE IN KEY RANGE ESTIMATES


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
CO   5770999  V7R3M0    MF62376   00/00    0000
CO   5770999  V7R3M0    MF61181   00/00    0000
CO   5770999  V7R3M0    MF61180   00/00    0000



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APAR Error Description / Circumvention

-----------------------------------------------
During optimization of a query, requests for selectivity
information from indexes can be obtained in the form of key
range estimate operations. In order to get accurate information
for a given predicate, the statistics manager may need to
evaluate a significant portion of an index's data. This
evaluation can take a long time for large indexes as index pages
are loaded into active memory and then analyzed.

In order to shorten the time required to optimize a query, the
statistics manager uses several different strategies when faced
with the need to perform a key range estimate.
One of the strategies is to cache prior estimates so that
subsequent requests for the same key range can be returned
quickly. Each index has a cache associated with it. Estimates
are stored in this cache until the cache fills or becomes stale
relative to the data in the index or until an IPL occurs. In
this case, it was determined that key ranges were being
invalidated too frequently (every couple of days) when in the
past, they were only invalidated after an IPL.

ADDITIONAL KEYWORDS: EKR

CORRECTION FOR APAR MA49095 :
-----------------------------
In some cases, a key range estimate operation may incorrectly
cause the key range estimate cache to shrink to its minimum size
of 100 entries. When this happens, valid estimates may be purged
from the cache, requiring additional key range processing if
those estimates are needed again.

This fix will prevent the incorrect behavior, allowing key range
estimate caches to grow to their intended size. This will
increase cached estimate re-use and reduce the number of key
range estimate operations for indexes affected by the incorrect
behavior.

CIRCUMVENTION FOR APAR MA49095 :
--------------------------------
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
--------------  ------------------------------------------------------------
   MF65604      LIC-DB-OTHER Query plan validation performance
   MF65044      OSP-DB-OTHER-LOOP JOB WILL NOT END, WAITING ON A SEIZE.
   MF65019      LIC-DB-OTHER-UNPRED Internal Database Maintenance
   MF64898      OSP SEIZING ISSUE WHEN MULTIPLE TASKS ARE PERFORMING ESTIMAT
   MF63539      OSP-PERFM INDEX NOT USED DUE TO INCORRECT 'IS NOT NULL' EKR
   MF62379      LIC-DB-OTHER Internal Database Maintenance.
   MF62223      LIC-DB-OTHER-WAIT Queries may hang during optimization
   MF61949      LIC-DB-OTHER-UNPRED Internal Database Maintenance
   MF61395      LIC-DB-OTHER Internal database maintenance
   MF61179      LIC-DB-OTHER Enable key range estimate operations to return

Summary Information

System..............................  i
Models..............................  
Release.............................  V7R3M0
Licensed Program....................  5770999
APAR Fixed..........................  View details for APAR MA49095
Superseded by:......................  
Recompile...........................  N
Library.............................  QSYS
MRI Feature ........................  NONE
Cum Level...........................  C2132730


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Document Information

Modified date:
24 May 2022