A fix is available
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 number
PH37932
Reported component name
IBM MQ Z/OS V9
Reported component ID
5655MQ900
Reported release
100
Status
CLOSED PER
PE
NoPE
HIPER
NoHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2021-06-07
Closed date
2022-02-18
Last modified date
2022-04-01
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
Fix is available
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Document Information
Modified date:
02 April 2022