PI86736: MQ V9: High CPU usage by a member of the queue-sharing group.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A Queue Manager of a QSG got high CPU usage when performing
  a CF structure backup.
  .
  Additional keywords/symptoms:
  CSQJW001 CSQJW107
  

Local fix

• n/a
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 0 Modification 0.                    *
  ****************************************************************
  * PROBLEM DESCRIPTION: When CSQ6LOGP is compiled with OUTBUFF  *
  *                      <= 100, the queue manager hangs if all  *
  *                      available log buffers are filled while  *
  *                      writing a log record to the queue       *
  *                      manager logs. High CPU usage can be     *
  *                      observed in the queue manager address   *
  *                      space, and in some cases the address    *
  *                      space of the application waiting for a  *
  *                      log record to be written.               *
  *                      This typically occurs when processing   *
  *                      a BACKUP CFSTRUCT command, due to the   *
  *                      large log record sizes involved.        *
  ****************************************************************
  While attempting to write a log record to the queue manager
  recovery logs, CSQJW001 detected that no log buffers were
  available. CSQJW001 resumes the log writer task to write out the
  contents of the log buffers up to a specified RBA, freeing up
  those buffers for reuse. The RBA specified must be prior than
  the RBA of the last complete log record written to the logs and
  so to ensure this is always the case, an RBA 17 control
  intervals prior to the current RBA is passed. However when
  OUTBUFF is less or equal to 100, and the log record is close to
  the 31K maximum size, the passed RBA has already been written
  out and the log writer returns immediately - no log buffers are
  written out and so CSQJW001 detects that there are still no
  available log buffers and resumes the log writer task again,
  passing the same RBA, and the log writer again completes without
  writing out any buffers. This repeats indefinitely, leading to
  high cpu in the queue manager address space, and the address
  space writing out the log record.
  Other tasks/applications attempting to write log records while
  this is occurring will suspend on the log writer latch.
  

Problem conclusion

• The minimum value of OUTBUFF is increased to 128, requiring up
  to 48K of additional private storage. This ensures the RBA
  required to be passed to the log writer task is always within
  the scope of the log buffer.
  To maintain compatibility, values of OUTBUFF less than 128 will
  be accepted, and will be treated internally as if a value of
  128 had been specified.
  
  The following page in the IBM MQ 9.0.0 Knowledge Center is
  updated:
  IBM MQ
   Configuring
    Configuring queue managers on z/OS
     Custominsing IBM MQ
      Task 17: Tailor your system parameter module
       Using CSQ6LOGP (q019310_.htm)
  
  The description of OUTBUFF is changed from
  "The parameter must be in the range 80 through 4000. The value
  specified is rounded up to a multiple of 4. Values between 40
  and 80 will be accepted for compatibility reasons, and will be
  treated as a value of 80."
  to
  "The parameter must be in the range 128 through 4000. The value
  specified is rounded up to a multiple of 4. Values between 40
  and 128 will be accepted for compatibility reasons, and will be
  treated as a value of 128."
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI52023

Modules/Macros

• CSQJS001
  

Fix information

• Fixed component name

  MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R000 PSY UI52023

     UP17/12/16 P F712 ¢

Fix is available

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