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MF61181 - LIC-DB-OTHER Enable key range estimate operations to return

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PTF ( Program Temporary Fixes ) Cover letter


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Abstract

LIC-DB-OTHER Enable key range estimate operations to return


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
CO   5770999  V7R3M0    MF61179   00/00    0000



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APAR Error Description / Circumvention

-----------------------------------------------
In order to select the best performing query plan, the SQL query
engine optimizer examines the data in indexes to determine how
many records a particular predicate may touch. These operations
are known as key range estimates. Query optimization must wait
for each estimate to complete before proceeding and before
running the query. On large data sets, these estimates can take
a long time, in some cases causing the length of the
optimization phase to exceed the length of the actual query
execution.

CORRECTION FOR APAR MA45200 :
-----------------------------
New function provided by this fix allows an index to return a
time-limited key range estimate quickly using one of several
approximation techniques. This reduces the time that the
optimizer spends working on the query and improves the
responsiveness of query execution. The amount of time that each
estimate takes is influenced by the KEY_RANGE_ESTIMATE_TIMEOUT
option which can be set in the active QAQQINI options file. Most
queries will not encounter this timeout. However, in the rare
cases when an estimate does reach its time limit, the estimate
will be sent to a background thread running in the QDBFSTCCOL
job, where it will be completed. This allows the currently
executing query to get a fast approximation quickly and ensures
that a more accurate estimate is available for later use by
other queries.

CIRCUMVENTION FOR APAR MA45200 :
--------------------------------
None.


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Supersedes

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

Summary Information

System..............................i
Models..............................
Release.............................V7R3M0
Licensed Program...............5770999
APAR Fixed..........................View details for APAR MA45200
Superseded by:......................
Recompile...........................N
Library.............................QSYS
MRI Feature ........................NONE
Cum Level...........................BASE


System i Support

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Document Information

Modified date:
22 March 2016