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DB2 - Problem description

Problem IC78123 Status: Closed

AN APPLICATION MAY APPEAR TO BE STUCK IN "UOW EXECUTING" STATE
WHEN EXECUTING A PLAN CONTAINING AN INDEX AND OPERATION.

product:
DB2 CONNECT / DB2CONNCT / 950 - DB2
Problem description:
An application may appear to be stuck in "UOW Executing" state 
when executing query with an execution plan that includes an 
index AND operation. It will be characterised by high CPU usage 
for one or more EDUs processing the query on behalf of the 
application. 
 
Index ANDing represents the logical AND of results from multiple 
index scans on the same source object to satisfy the filtering 
criteria or to merge the results of semi-joins used in star 
joins. 
 
Examination of the stack for an EDU involved in this processing 
will be similar to the following: 
========================================== 
sqlri_BFBandP 
sqliScanLeaf2NoLocking 
sqlifnxt 
sqlirdk 
sqldIndexFetch 
sqldIndexFetch 
sqldRowFetch 
...... 
========================================== 
 
The application isn't truly hung but may take an unrealistic 
amount of time to complete and may be forced using the FORCE 
APPLICATION command.
Problem Summary:
**************************************************************** 
* USERS AFFECTED:                                              * 
* All users of version 9.5 on Linux, Unix and Windows          * 
* platforms.                                                   * 
**************************************************************** 
* PROBLEM DESCRIPTION:                                         * 
* An application may appear to be stuck in "UOW Executing"     * 
* state when executing query with an execution plan that       * 
* includes an index AND operation. It will be characterised by * 
* high CPU usage for one or more EDUs processing the query on  * 
* behalf of the application.                                   * 
*                                                              * 
* Index ANDing represents the logical AND of results from      * 
* multiple index scans on the same source object to satisfy    * 
* the filtering criteria or to merge the results of semi-joins * 
* used in star joins.                                          * 
*                                                              * 
* Examination of the stack for an EDU involved in this         * 
* processing will be similar to the following:                 * 
* ==========================================                   * 
* sqlri_BFBandP                                                * 
* sqliScanLeaf2NoLocking                                       * 
* sqlifnxt                                                     * 
* sqlirdk                                                      * 
* sqldIndexFetch                                               * 
* sqldIndexFetch                                               * 
* sqldRowFetch                                                 * 
* ......                                                       * 
* ==========================================                   * 
*                                                              * 
* The application isn't truly hung but may take an unrealistic * 
* amount of time to complete and may be forced using the FORCE * 
* APPLICATION command.                                         * 
**************************************************************** 
* RECOMMENDATION:                                              * 
* Upgrade to DB2 LUW Version 9.5 FixPak 9 or higher levels.    * 
****************************************************************
Local Fix:
Use the query explain tools to check the access plan for the 
executing SQL and create necessary indices to avoid the index 
AND operations.
available fix packs:
DB2 Version 9.5 Fix Pack 9 for Linux, UNIX, and Windows
DB2 Version 9.5 Fix Pack 10 for Linux, UNIX, and Windows

Solution
First fixed in DB2 LUW Version 9.5 FixPak 9.
Workaround
Use the query explain tools to check the access plan for the 
executing SQL and create necessary indices to avoid the index 
AND operations.
BUG-Tracking
forerunner  : APAR is sysrouted TO one or more of the following: IC78143 
follow-up : 
Timestamps
Date  - problem reported    :
Date  - problem closed      :
Date  - last modified       :
14.08.2011
12.03.2012
12.03.2012
Problem solved at the following versions (IBM BugInfos)
9.0.,
9.5.
Problem solved according to the fixlist(s) of the following version(s)
9.5.0.9 FixList
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