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DB2 - Problembeschreibung

Problem IC64000 Status: Geschlossen

IN DB2 LUW, YOU MAY ENCOUNTER POOR PERFORMANCE OF QUERY WITH CORRELATED
NLJOIN OUTER LEG

Produkt:
DB2 FOR LUW / DB2FORLUW / 970 - DB2
Problembeschreibung:
The DB2 SQL Optimizer may choose a less-than-optimal access 
plan in cases where an SQL query contains one or more complex 
   correlated Nested Loop Joins (NLJOIN). The following is an 
  example of a query that could result in an access plan that 
 contains a complex correlated NLJOIN: 
SELECT * FROM T1 WHERE EXISTS(SELECT 1 FROM T2, T3 WHERE T1.C1 
=T2.C1 and T2.C2 = T3.C2) 
 
You are likely to experience this problem if the following 
conditions are met: 
 
1. When the db2exfmt output, Control Center Visual Explain, or 
Optimum Query Tuner Query Access Plan is examined, the 
correlated predicate is placed on the outer leg (left input) of 
a NLJOIN, and is applied using an Index Scan (IXSCAN) applying 
the predicate(s) as a Start/Stop key against the index. 
 
2. The Start/Stop Predicates must filter the index down to a 
small subset of the values in the index. 
 
3. The index must contain more than 1 page. The larger the 
index, the more likely you are to encounter this problem.
Problem-Zusammenfassung:
**************************************************************** 
* USERS AFFECTED:                                              * 
* ALL                                                          * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* The DB2 SQL Optimizer may choose a less-than-optimal access  * 
*                                                              * 
* plan in cases where an SQL query contains one or more        * 
* complex                                                      * 
*    correlated Nested Loop Joins (NLJOIN). The following is   * 
* an                                                           * 
*   example of a query that could result in an access plan     * 
* that                                                         * 
*  contains a complex correlated NLJOIN:                       * 
*                                                              * 
* SELECT * FROM T1 WHERE EXISTS(SELECT 1 FROM T2, T3 WHERE     * 
* T1.C1                                                        * 
* =T2.C1 and T2.C2 = T3.C2)                                    * 
*                                                              * 
*                                                              * 
*                                                              * 
* You are likely to experience this problem if the following   * 
*                                                              * 
* conditions are met:                                          * 
*                                                              * 
*                                                              * 
*                                                              * 
* 1. When the db2exfmt output, Control Center Visual Explain,  * 
* or                                                           * 
* Optimum Query Tuner Query Access Plan is examined, the       * 
*                                                              * 
* correlated predicate is placed on the outer leg (left input) * 
* of                                                           * 
* a NLJOIN, and is applied using an Index Scan (IXSCAN)        * 
* applying                                                     * 
* the predicate(s) as a Start/Stop key against the index.      * 
*                                                              * 
*                                                              * 
*                                                              * 
* 2. The Start/Stop Predicates must filter the index down to a * 
*                                                              * 
* small subset of the values in the index.                     * 
*                                                              * 
*                                                              * 
*                                                              * 
* 3. The index must contain more than 1 page. The larger the   * 
*                                                              * 
* index, the more likely you are to encounter this problem.    * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to Version 9.7 Fix Pack 1.                           * 
****************************************************************
Local-Fix:
n/a
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 was first fixed in Version 9.7 Fix Pack 1. At a 
minimum, this fix should be applied at the server.
Workaround
keiner bekannt / siehe Local-Fix
Weitere Daten
Datum - Problem gemeldet    :
Datum - Problem geschlossen :
Datum - der letzten Änderung:
22.10.2009
24.02.2010
24.02.2010
Problem behoben ab folgender Versionen (IBM BugInfos)
9.7.FP1
Problem behoben lt. FixList in der Version
9.7.0.1 FixList