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DB2 - Problembeschreibung

Problem IC72243 Status: Geschlossen

Optimizer may choose a non-optimal plan for queries using FETCH FIRST ROWS
ONLY caluse, which can cause performance degradation.

Produkt:
DB2 FOR LUW / DB2FORLUW / 970 - DB2
Problembeschreibung:
Optimizer may choose a non-optimal plan for queries using FETCH 
FIRST ROWS ONLY (FFNR) caluse, which can lead to performance 
degradation. This plan causes a large stream of data to be 
broadcasted across partitions. Users will find this evident in 
the query access plan, which will show the BTQ operation 
broadcasting large stream of data as following: 
 
             /-------- 
       1.07181e+07 
         BTQ 
         (  13) 
         125531 
         31015.2 
           | 
       2.67952e+06 
         IXSCAN 
         (  14) 
         123504 
         31015.2 
           | 
       2.67952e+06 
     INDEX: <name of the index> 
 
In this example, aprox 1.07x10^7 rows are being broadcasted 
across partitions. This leads to poor performance.
Problem-Zusammenfassung:
USERS AFFECTED: 
=============== 
Customer using version 9.5 and above on all platforms. 
 
PROBLEM DESCRIPTION: 
==================== 
Queries using FIRST FIRST ROWS ONLY (FFNR) clause may experience 
performance problem after migrating from version 8 to version 9. 
The APAR can be confirmed by checking the query access graph. If 
a BTQ operation is seen broadcasting large stream of data, it 
may point to this APAR. 
 
RECOMMENDATION: 
=============== 
There is currently no workaround other than not using the FFNR 
clause.
Local-Fix:
verfügbare FixPacks:
DB2 Version 9.7 Fix Pack 4 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 5 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 6 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 7 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 8 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 10 for Linux, UNIX, and Windows

Lösung
Problem is first fixed in version 9.7 Fixpack 4.
Workaround
There is currently no workaround other than not using the FFNR 
clause.
Weitere Daten
Datum - Problem gemeldet    :
Datum - Problem geschlossen :
Datum - der letzten Änderung:
27.10.2010
03.05.2011
03.05.2011
Problem behoben ab folgender Versionen (IBM BugInfos)
9.7.FP4
Problem behoben lt. FixList in der Version
9.7.0.4 FixList