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MF61632 - LIC-DB-OTHER-LOOP A query predicate with multiple large NOT

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Abstract

LIC-DB-OTHER-LOOP A query predicate with multiple large NOT


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
NONE



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APAR Error Description / Circumvention

-----------------------------------------------
Under certain circumstances, a query with a predicate having
multiple NOT IN lists will appear to be stuck in a loop during
optimization. The call stack will frequently show
DBSTMDPREDICATERANGEINFO at the top. A job stuck in this loop
can not be ended.

CORRECTION FOR APAR MA45358 :
-----------------------------
The factors which precipitate this behavior are: (1) a
select/omit keyed logical file or an index containing selection
predicates that reference a particular column; (2) a query with
a predicate containing two large NOT IN lists--one list
comparing to the column in (1) and one list comparing to a cast
of that column; and (3) both NOT IN lists containing a large
number of values. Under these circumstances, the algorithm that
the statistics engine uses to match the query predicate to the
logical file/index experiences execution time growth that is
exponential in relation to the size of the NOT IN lists. This
behavior is working as designed, and the loop will eventually
end.
This fix will make the query cancel-able.

CIRCUMVENTION FOR APAR MA45358 :
--------------------------------
Users may wish to rewrite their queries to avoid at least one of
the factors noted in the problem conclusion.


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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 MA45358
Superseded by:......................
Recompile...........................N
Library.............................QSYS
MRI Feature ........................NONE
Cum Level...........................C7061730


System i Support

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Document Information

Modified date:
03 August 2016