PI25337: NO RESPONSE AND HIGH CPU AFTER DEFINE/DELETE PAGESET, AND BUFFERPOOL SEVERAL TIMES IN THE SAME RUN OF QMGR.

Obtain the fix for this APAR.

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 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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