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MF64512 - OSP-OTHER-PERFM QUERY PERFORMS POORLY WHEN SKEWED DATA IS PR

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PTF ( Program Temporary Fixes ) Cover letter


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Abstract

OSP-OTHER-PERFM QUERY PERFORMS POORLY WHEN SKEWED DATA IS PR


Pre/Co-Requisite PTF / Fix List

REQ  LICENSED           PTF/FIX  LEVEL

TYPE PROGRAM  RELEASE   NUMBER   MIN/MAX  OPTION
---- -------- --------- -------  -------  ------
PRE  5770999  V7R3M0    MF63963   00/00    0000
PRE  5770999  V7R3M0    MF63247   00/00    0000
PRE  5770999  V7R3M0    MF61285   00/00    0000
CO   5770999  V7R3M0    MF64511   00/00    0000
CO   5770999  V7R3M0    MF64007   00/00    0000
CO   5770999  V7R3M0    MF64008   00/00    0000
CO   5770999  V7R3M0    MF64009   00/00    0000
CO   5770999  V7R3M0    MF64010   00/00    0000
CO   5770999  V7R3M0    MF63346   00/00    0000
CO   5770999  V7R3M0    MF62833   00/00    0000
CO   5770999  V7R3M0    MF62178   00/00    0000



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APAR Error Description / Circumvention

-----------------------------------------------
A DELETE query, that is not going into pseudo-open mode, is
performing poorly when the host variable value changes to a
highly skewed data value.

CORRECTION FOR APAR MA46572 :
-----------------------------
Most select statements with host variables that present highly
skewed data values (and thus data result sets) get a chance to
"self correct" the plan in real time via AQP (adaptive query
processing added in 7.1).  Delete queries (this problem concern)
however are not plugged in to the AQP handler interface. Other
than via AQP, the primary way the optimizer  reconsiders the
plan per a changed set of host variable values and thus expected
results is at full open time provided the optimization time
compared to the current known runtimes (up to that point) makes
a re-optimization seem like a "reasonable" thing  to do.  The
optimizer doesn't want to optimize unnecessarily.   In this
particular case, however the existing known runtimes were tiny,
the optimization times was not trivial and so a full open didn't
consider the current host vars and a potentially better plan
given what was known about prior runs.   Because AQP doesn't
kickin for deletes and because full open fell in to logic that
simulated optimization  only when required, the customer was
left with a locked in poor plan (for these skewed host vars).
The change here was to give updateable queries like this DELETE
request, that doesn't play in the AQP space, more leeway at
validate plan time on full opens so that simulated only required
gets a chance to consider more runs ...before going in to that
simulate only require mode.   The leeway is again, a static,
allowing more consideration.  Whether that leeway is broad
enough will be determined from feedback on problems like this.

CIRCUMVENTION FOR APAR MA46572 :
--------------------------------
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
--------------  ------------------------------------------------------------
   MF64407      LIC-DB-UNPRED Query referencing freed storage after vlog
   MF64291      OSP-PERFM SQL BAD ESTIMATE AQP
   MF64271      LIC-DB-OTHER-UNPRED Internal Database Maintenance
   MF64076      OSP-DB-OTHER-F/DBOPEXPRQDSX/01FE88-T/QQQOOODBOPX/5118- MSGMC
   MF64006      LIC-DB-OTHER Internal Database Maintenance.
   MF63945      LIC-DB-PERFM reorder predicates based on selectivity
   MF63924      OSP-INCORROUT PLANCACHE SNAPSHOT MISSES 'PLAN CREATION USER
   MF63767      LIC-DB-OTHER-F/DBOPRELTABLEMISC-T/QDBGETMQO-MSGMCH3203 MSGMC
   MF63538      OSP-DB-OTHER-F/DBOPRELTABLEMISC-T/QQQOOODBOPX/5000 SELECT ST
   MF63411      OSP-DB-OTHER-F/IXMACHINEINDEXEXTEND-T/QDBPUTMX-MSGMCH2804 MS
   MF63403      OSP-OTHER-PERFM IMPROVEMENT TO PSEUDO_OPEN_CHECK_HOST_VARS Q
   MF63374      LIC-DB Internal maintenance
   MF63345      LIC-DB-Other Improve AQP Error Handling
   MF63341      LIC-DB Improve AQP's ability to re-optimize LPG plans
   MF63297      LIC-DB Internal Maintenance
   MF62179      LIC-DB-OTHER-F/DBLISTHOME-T/QQQOOODBOP-MSGMCH0601 A COMPLEX
   MF63225      LIC-DB-OTHER-PERFM SQL GETTING HARD CLOSED REASON CODE IN DB
   MF63158      OSP-OTHER-PERFM QUERY RE-OPTIMIZATIONS OCCURRING
   MF63149      OSP-DB-OTHER-SRCB6XX0302-UNPRED AQP THREADS CORRUPTING THE S
   MF63148      LIC-DB-OTHER-INCORRECT INAVIGATOR PLAN CACHE ANALYSIS OF ACC
   MF62831      LIC-DB-OTHER-PERFM Reduce the system overhead for QSYS2/SYSI
   MF62814      LIC-DB-OTHER Internal maintenance
   MF62755      LIC-DB-UNPRED Failure tracing Query
   MF62645      OSP-DB-OTHER-F/DBPMTRAP-T/QDBGETM-MSGMCH3203 MSGMCH3203 F/DB
   MF62560      OSP-DB-PERFM Unnecessary hard close of open data path for qu
   MF62522      LIC-DB-OTHER-PERFM REMOVE CORRECT PLAN FROM PLAN CACHE
   MF62516      LIC-DB-OTHER Unable to VE very complex plan from Plan Cache
   MF62458      LIC-DB-OTHER IS NULL index advice ordering.
   MF62382      LIC-DB-OTHER Internal Maintenance
   MF61335      LIC-DB Internal Maintenance
   MF62302      LIC-DB-PERFM SMP support for OLAP queries
   MF61932      LIC-DB-OTHER Internal database maintenance
   MF62182      LIC-DB-OTHER-THREADS-PERFM SYSTEM PERFORMANCE AFFECTED BY AQ
   MF62182      LIC-DB-OTHER-PERFM INFLUX OF QUERY REOPTIMIZAITONS
   MF62061      LIC-DB-OTHER-PERFM QUERY PERFORMS POORLY DUE TO BAD STATISTI
   MF61931      OSP-DB-OTHER-WAIT SUPERVISOR HEAP GROWTH DUE TO PENDING SIGN
   MF61877      LIC-DB-OTHER-UNPRED SQE ROQ USAGE IN PLAN CACHE GROWING DAIL
   MF57967      LIC-DB-PERFM Improve re-use of temporary results with Concur
   MF61787      OSP-DB-OTHER-F/DBOPEXPRQDS-T/QQQOOODBOP-MSGMCH3203 VL0600BAD
   MF61787      OSP-DB-OTHER OUTPUT QRO HASH OF QUERY INITIATING MTI IN TRAC
   MF61208      OSP-PAR-940XBASE ALLOW REMOVAL OF NON-SHAREABLE MTIS IN A MO
   MF61208      OSP-PAR-940XBASE ALLOW REMOVAL OF NON-SHAREABLE MTIS IN A MO
   MF61662      F/DBOPEXPRVALMISC-MSGMCH3203 R720 MCH3203 T/QQQOOOUPCL F/DBO
   MF61289      LIC-DB Offload long EKR estimates found during optimization
   MF61218      OSP-INCORROUT VISUAL EXPLAIN 3 OF TIMESTAMPS ARE INCORRECT.
   MF61188      LIC-DB-OTHER-UNPRED QUERY/400 MAY USE LARGE AMOUNTS OF TEMPO
   MF61188      LIC-DB-OTHER-MSGMCH1202 WHEN BLANK RECORDS RETURNED FROM SQL
   MF61188      OSP-DB SYSTEM CRASH WITH SRCB6000302
   MF61188      LIC-DB-OTHER-PERFM SQE OPTIMIZER AQP FUNCTIONALITY SUBSTITUT
   MF60945      OSP-OTHER-PERFM LONG OPTIMIZATION TIME DUE TO NUMEROUS UDFS/

Summary Information

System..............................  i
Models..............................  
Release.............................  V7R3M0
Licensed Program....................  5770999
APAR Fixed..........................  View details for APAR MA46572
Superseded by:......................  View fix details for PTF MF71218
Recompile...........................  N
Library.............................  QSYS
MRI Feature ........................  NONE
Cum Level...........................  C8242730


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Document Information

Modified date:
13 September 2023