A fix is available
APAR status
Closed as program error.
Error description
DGTT mass delete performance enhancement. SQLDGTT DB2MIGV9/K
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: Users of Declared Global Temp Tables (DGTTs) * * in DB2 V9. * **************************************************************** * PROBLEM DESCRIPTION: (1) Uncommitted DGTT mass-deletes in * * V9 caused performance degradation * * for subsequent DGTT insert/delete * * operations. * * (2) When the ON COMMIT PRESERVE ROWS * * option is in effect for DGTTs, * * segments mass-deleted within the * * same commit-scope were not reused * * after commit. * * (3) DGTTs get SQLCODE -904 more often * * in V9, due to lack of needed space, * * than in V8. * **************************************************************** * RECOMMENDATION: * **************************************************************** Mass-deleted DGTT segments remained on the segment chain until commit or rollback and caused increased overhead for subsequent insert/delete operations. For DGTT's with the ON COMMIT PRESERVE ROWS option, segments mass-deleted within the same commit-scope were not reused after commit. DGTTs get SQLCODE -904 more often in V9 than in V8 for lack of needed space due to the fact that DGTTs had their own TEMP data base prior to V9, but in V9 they compete for space with work files in the WORKFILE data base; and DGTTs (unlike work files) cannot span across multiple table spaces.
Problem conclusion
Code has been optimized (1) to provide significant performance improvement with DGTT mass-deletes, (2) to reuse the space occupied by mass-deleted rows at commit for DGTTs with ON COMMIT PRESERVE ROWS option, and (3) to minimize contention for space between work files and DGTTs, by implementing a preference in the selection of table spaces that cannot grow beyond the primary space allocation (due to SECQTY = 0) for work files use, and a preference in the selection of table spaces that can grow beyond the primary space allocation (with SECQTY > 0) for DGTT use (please note that this enhancement only takes effect on DB2-managed table spaces, not user-managed). Some changes will be made in DB2 publications to go with this APAR fix. Customers are advised to follow the recommendations listed in the publication changes, which are documented in the Tracking Comments. Please see the Tracking Comments data for details. While DDL can always be used to create table spaces in the work file database, this can also be accomplished by using the DSNTWFG installation program. For information on how DSNTWFG can be modified to create table spaces in the work file database with a preferred value for secondary quantity, technote 1386786 is being prepared, currently titled "How can I make DSNTWFG create work file table spaces with an explicit SECQTY?". Changes in DB2 publications : ---------------------------------------------------------------- 1. Performance Monitoring and Tuning Guide : 1A. The following text will be added to the section "Creating additional work file table spaces" of Performance Monitoring and Tuning Guide : It is strongly advised that multiple table spaces with zero secondary quantity be defined for work files use in the WORKFILE data base. DB2 gives preference to table spaces with zero secondary quantity when allocating space for work files. Multiple work file table spaces help in supporting efficient concurrent read and write I/O's to work files. If applications use Declared Global Temporary Tables (DGTTs), it is also advised that some table spaces be defined with non-zero secondary quantity in the WORKFILE data base. This will minimize contention for space between work files and DGTTs, since DB2, when allocating space for DGTTs, gives preference to table spaces that can grow beyond the primary space allocation (with SECQTY > 0), since DGTTs are limited to one table space and cannot span multiple table spaces as the work files can. If there will be no DGTTs, then it is better that all table spaces are defined with zero secondary quantity. Depending on the number of table spaces and the amount of concurrent activity, performance can vary. In general, adding more table spaces improves the performance. One may have to fine-tune the combination of different types of table spaces in the workfile database. ---------------------------------------------------------------- ---------------------------------------------------------------- 1B. In section "How sort work files are allocated" of Performance Monitoring and Tuning Guide, the sentence "When your application needs to sort data, the work files are allocated on a least recently used basis for a particular sort." will be changed to "When your application needs to sort data, DB2 will try to allocate each sort work file on a table space that has no secondary allocation (SECQTY = 0) and is least recently used. When table spaces with the preferred features are not available, then any available table space will be used." ----------------------------------------------------------------
Temporary fix
********* * HIPER * *********
Comments
APAR Information
APAR number
PK70060
Reported component name
DB2 OS/390 & Z/
Reported component ID
5740XYR00
Reported release
910
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt
Submitted date
2008-08-04
Closed date
2009-05-22
Last modified date
2011-02-19
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UK46839
Modules/Macros
DSNDCT DSNDLKNM DSNDPSFI DSNDSEG DSNDWACT DSNDWFPL DSNIBWAC DSNICMT2 DSNIGWAC DSNISEGD DSNISEGF DSNISGNS DSNITNPG DSNIWCUB DSNIWKFL DSNWDFDM
Fix information
Fixed component name
DB2 OS/390 & Z/
Fixed component ID
5740XYR00
Applicable component levels
R910 PSY UK46839
UP09/06/09 P F906
Fix is available
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Document Information
Modified date:
19 February 2011