PH37932: CHECKPOINT(QJSTLLCP) IS COUNTED TWICE INCORRECTLY WHEN FILLING AN ACTIVE LOG.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When using dual logging, and checkpoints initiated due to
  active log switching,  QJSTLLCP is incremented incorrectly.
  A change was made in MQ V900 GA which extended the scenarios in
  which QJSTLLCP is incremented, to include checkpoints initiated
  due to active log switching. The intention was that QJSTLLCP
  would be a count of all checkpoints in an SMF interval,
  regardless of whether they were issued due to LOGLOAD or active
  log switching.
  
  The end of log code (CSQJW307) is called once for each log
  copy, and sets a flag in the global LMB control block. The next
  log record to be written will then initiate an increment of
  QJSTLLCP and the start of a checkpoint. This gives rise to a
  timing window when using dual logging, whereby a log record is
  written between the two CSQJW307 calls, which will result in
  QJSTLLCP being incremented twice.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of IBM MQ for z/OS Version 9       *
  *                 Release 1 Modification 0 and Release 2       *
  *                 Modification 0.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: When checkpoints are initiated due to   *
  *                      active log switching, it is possible    *
  *                      for QJSTLLCP to be incremented          *
  *                      incorrectly.                            *
  ****************************************************************
  The code that increments QJSTLLCP included a timing window,
  whereby when using dual logging it was possible that following
  an active log switch both log copy 1 and log copy 2 increment
  QJSTLLCP.
  
  Another scenario meant it was also possible for QJSTLLCP to not
  be incremented at all when using either single or dual logging
  if competing threads try to increment the value.
  

Problem conclusion

• The code has changed to ensure QJSTLLCP is incremented
  consistently when checkpoints are initiated due to active log
  switching.
  

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:

  UI79409 UI79410

Modules/Macros

• CSQJW001 CSQRCPRC
  

Fix information

• Fixed component name

  IBM MQ Z/OS V9

• Fixed component ID

  5655MQ900

Applicable component levels

• R100 PSY UI79410

     UP22/03/11 P F203

• R200 PSY UI79409

     UP22/03/11 P F203

Fix is available

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