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DB2 - Problembeschreibung

Problem IC61598 Status: Geschlossen

THE DB2 QUERY OPTIMIZER MAY UNDERESTIMATE THE JOIN COST, POTENTIALLY
LEADING TO A SUB-OPTIMAL QUERY ACCESS PLAN

Produkt:
DB2 FOR LUW / DB2FORLUW / 970 - DB2
Problembeschreibung:
If your SQL statement contains an equality join predicate 
between two tables, such as the one in the WHERE clause in 
the following example 
. 
  SELECT ... 
  FROM T1, T2 ... 
  WHERE ... T1.COLUMN1 = T2.COLUMN2 ... 
. 
and distribution statistics are collected, the optimizer could 
take advantage of the distribution statistics in combination 
with the high2key and low2key statistics during join cost 
computation. 
. 
If the number of distinct values in either COLUMN1 or COLUMN2 
is less than 3, then the optimizer may underestimate the cost 
of the join. 
. 
The number of distinct values is described by the COLCARD column 
in the SYSSTAT.COLUMNS catalog view.
Problem-Zusammenfassung:
see APAR text.
Local-Fix:
1) Use an optimizer profile to force the desired access plan, OR 
2) Update the LOW2KEY of the column with the smaller number of 
   distinct values to the LOW2KEY of the column with the higher 
   number of distinct values.
verfügbare FixPacks:
DB2 Version 9.7 Fix Pack 1 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 2 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 3 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 3a for Linux, UNIX, and Windows
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 7 for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 9a for Linux, UNIX, and Windows
DB2 Version 9.7 Fix Pack 6 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 10 for Linux, UNIX, and Windows

Lösung
Problem first fixed in DB2 UDB 9.7 Fixpack 1.
Workaround
see APAR text
Weitere Daten
Datum - Problem gemeldet    :
Datum - Problem geschlossen :
Datum - der letzten Änderung:
19.06.2009
04.02.2010
04.02.2010
Problem behoben ab folgender Versionen (IBM BugInfos)
9.7.FP1
Problem behoben lt. FixList in der Version
9.7.0.1 FixList