A fix is available
APAR status
Closed as program error.
Error description
DISCARDDATA of REAL STORAGE frames results in RSM serialization to manage the frame status and page faults for those frames which were unbacked with KEEPREAL(NO). The combination of these on an LPAR where paging typically does not occur, results in significant cpu overhead.
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: All DB2 10 users. * **************************************************************** * PROBLEM DESCRIPTION: Frequent thread terminations without * * re-use may result in significant CPU * * consumption as 64bit thread pool * * storage is freed and REAL frames are * * unbacked. * **************************************************************** * RECOMMENDATION: * **************************************************************** When threads terminate, their pool storage may either be completely freed if the thread is not cached for reuse, or a portion may be freed. In either case, storage which is only virtually freed by DB2 since it is submanaged, will have its REAL frames unbacked in many cases. This unbacking requires RSM latch serialization and also results in a pagefault when those pages are again used. This whole process can show significant CPU usage depending on the number of threads and their allocation/deallocation frequency. Similarly, thread contraction which may occur at specific commit frequencies, also may result in pool storage being virtually freed with the REAL frames unbacked. REALSTORAGE_MANAGEMENT which has default of AUTO, should not result in the discard of REAL frames unless the LPAR comes under stress and begins paging or nears the REALSTORAGE_MAX value if specified.
Problem conclusion
This apar changes the way 64 bit Above-the-bar (ATB) real storage frames are managed by DB2 based on the DB2 zparms REALSTORAGE_MANAGEMENT,REALSTORAGE_MAX and general RSM LPAR storage monitor fields. DB2 ATB storage management is changed to no longer issue an IARV64 DISCARDDATA request to free real storage frames unless the DB2 storage monitor has detected that DISCARD MODE should be turned ON. When DISCARD MODE is ON the member will return to the same behavior it had prior to PM88804 and issue an IARV64 DISCARDDATA request when freeing storage. Not freeing the real storage frames can improve system performance due to a significant reduction in first reference page faults, RSM lock contention, and uncaptured CPU time. *** NOTE *** PM88804 may result in higher REAL FRAME counts being reported by DB2 monitor reports and RMF, especially in environments that never page to aux. For those customers who experience frequent or periodic paging, the counts may not be significantly higher but will likely still be higher than before PM88804. PM88804 reverses some of the affect of PK25427. The major reporting fields for 64 bit storage are: qw0225ShrStg_Real - Shared storage most heavily used for threads will likely show the most increase. qw0225ComStg_Real - High Common qw0225PriStg_Real - High address space private
Temporary fix
Comments
APAR Information
APAR number
PM88804
Reported component name
DB2 OS/390 & Z/
Reported component ID
5740XYR00
Reported release
A10
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt
Submitted date
2013-05-10
Closed date
2013-06-24
Last modified date
2013-07-02
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
UK95350
Modules/Macros
DSNSCON2 DSNSVSFM DSNSVSPC DSNSVSVP
Fix information
Fixed component name
DB2 OS/390 & Z/
Fixed component ID
5740XYR00
Applicable component levels
RA10 PSY UK95350
UP13/06/29 P F306
Fix is available
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Document Information
Modified date:
02 July 2013