A fix is available
APAR status
Closed as program error.
Error description
The customer added a new pageset 7 with new buffer pool 7 to queue manager CSQ1 dynamically using define command "DEFINE PSID BUFFPOOL(7) DSN(MY.PSID07) EXPAND(USER)" and "ALTER BUFFPOOL(7) BUFFERS(2000)" using CSQUTIL. . After definition was done, the customer tried to remove the pageset again with DELETE PSID. But the pageset 7 wasn't removed. Instead, there was a high cpu consumption of this queue mananger. . The change team has identified the issue which caused the high CPU and prevented the queue manager (qmgr) from stopping in this case. . The problem happens when a particular bufferpool and pageset are defined and deleted more than once during a run of the qmgr. When the bufferpool is deleted, some state for that bufferpool number is left in the qmgr control blocks. When a new bufferpool is defined with the same bufferpool number, the residual state causes the bufferpool's Deferred Write Processor worker task to terminate prematurely. . Without this task running, updated pages in the bufferpool will not be written back to the pageset. This could cause several symptoms, including a shortage of available buffers in the pool. . In the customer's case, the symptom seen was caused by the subsequent DELETE PSID command for a pageset using the problem bufferpool. The delete command tries to trigger the buffer pool's DWP task to flush updated pages for the pageset before it is deleted. Since the DWP task is not running, the DELETE PSID processing loops waiting for all its pages to be flushed. This is the process using the high CPU in the dump, and would also be the reason that the qmgr would not terminate normally.
Local fix
Problem summary
**************************************************************** * USERS AFFECTED: All users of WebSphere MQ for z/OS Version 7 * * Release 1 Modification 0. * **************************************************************** * PROBLEM DESCRIPTION: A command to delete a page set hangs * * and the queue manager uses high CPU. * * The queue manager does not respond to * * stop commands and needs to be * * cancelled. * **************************************************************** * RECOMMENDATION: * **************************************************************** When a given page set is deleted, it causes deferred write processor tasks for buffer pools relating to the page set to be stopped. This is done by setting the fTermDWP flag for the relevant tasks. This flag is not reset, causing a subsequent deferred write processor task for that particular buffer pool number to be immediately stopped. If another attempt is made to stop the task, a tight loop will occur in CSQP9DWS and CSQPFSET. Note that the reuse of the buffer pool number and deferred write processor task needs to happen during the same run of the queue manager for the problem to occur.
Problem conclusion
The code was changed to correctly reset the shutdown flag for the deferred write processor task when it stops. 100Y CSQP1DWP
Temporary fix
********* * HIPER * *********
Comments
APAR Information
APAR number
PI25337
Reported component name
WMQ Z/OS V7
Reported component ID
5655R3600
Reported release
100
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2014-09-09
Closed date
2014-10-15
Last modified date
2014-12-01
APAR is sysrouted FROM one or more of the following:
APAR is sysrouted TO one or more of the following:
PI27096 UI22204
Modules/Macros
CSQP1DWP
Fix information
Fixed component name
WMQ Z/OS V7
Fixed component ID
5655R3600
Applicable component levels
R100 PSY UI22204
UP14/11/13 P F411 ¢
Fix is available
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Document Information
Modified date:
01 December 2014