PH14812: CPSM SYSPLEX OPTIMISED WORKLOAD MANAGEMENT RESULTS IN HIGH CF USAGE WHEN RUNNING WITH VERY HIGH MXT VALUES

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A CICSPlex SM Sysplex Optimised Workload shares region status
  data in the z/OS coupling facility with access controlled by
  a coupling facility data table (CFDT) server.
  This information describes the health status and load of each
  region participating in the workload. Target regions typically
  update their own record in this CFDT when the current task load
  crosses certain tier boundaries. The size of these boundaries
  is controlled by the UPDATERS setting. The size of the lowest
  boundary is controlled by the BOTRSUPD setting, which by
  default is 1% of MXT.
  
  For CICS regions running with a very high MXT setting, which
  spend a significant amount of time operating below 1% of MXT,
  this may result in an unusually high rate of updates to
  coupling facility data table DFHRSTAT.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of CICSPlex SM V5.4, V5.5, V5.6.   *
  ****************************************************************
  * PROBLEM DESCRIPTION: CICS regions using CICSPlex SM          *
  *                      Optimised Workload Management with      *
  *                      a high MXT value but low number of      *
  *                      concurrent tasks may result in high     *
  *                      rate of coupling facility data table    *
  *                      DFHRSTAT updates.                       *
  *                      This occurs when WLM target regions     *
  *                      spend a significant amount of time      *
  *                      operating below the BOTRSUPD threshold. *
  ****************************************************************
  * RECOMMENDATION: After applying the PTF resolving this APAR,  *
  *                 all target regions must be restarted to      *
  *                 pickup the changes. Note that the restarts   *
  *                 do not need to occur at the same time.       *
  *                                                              *
  *                 Target regions wishing to exploit the new    *
  *                 function should specify new feature toggle:  *
  *                 com.ibm.cics.cpsm.wlm.botrsupd.enabled=false *
  *                 however a tuning exercise should first       *
  *                 be undertaken to assess the number of        *
  *                 target regions available, the MXT values,    *
  *                 and the expected level of work.              *
  ****************************************************************
  When using CICSPlex SM Sysplex Optimised Workload Management,
  every task load change below the BOTRSUPD threshold in a target
  region will cause an update to the CICS region status (RS)
  server (DFHRSTAT). The default value for BOTRSUPD is 1% of the
  MXT value; this is also the minimum value.
  Therefore, CICS regions running with a high MXT setting, and a
  consistently low number of concurrent tasks may result in a high
  rate of updates to the CICS RS server.
  

Problem conclusion

• A new feature toggle has been added to let users control whether
  or not to update the CICS RS server when the task load remains
  below the BOTRSUPD threshold.
  The new feature toggle is:
  com.ibm.cics.cpsm.wlm.botrsupd.enabled = { TRUE | false }
  
  The default setting (true) will maintain the current behaviour.
  When this feature toggle is set to false, then DFHRSTAT will not
  be updated for task load changes below the BOTRSUPD threshold.
  The apparent task load (ROUTINGLOAD as seen through the WLMATARG
  resource table) will remain at zero tasks, until the first
  boundary defined by the UPDATERS setting is reached.
  Note that if only a subset of target regions within a workload
  are run with com.ibm.cics.cpsm.wlm.botrsupd.enabled=false, then
  those regions may take a greater proportion of the workload.
  
  The feature toggle is only meaningful in a MAS which is a
  target region in an active workload. In all other contexts it
  will be ignored.
  
  Modules DFHRSDC, DFHRSDM, DFHRSXM have been updated to support
  this new feature.
  
  
  The Knowledge Center for CICS Transaction Server for z/OS
  Version 5 Release 4, Version 5 Release 5, and Version 5 Release
  6  will be updated.
  
  A new entry will be added to the 'Changes to toggle-enabled'
  features topic.
  Feature Name: Disable updates to the coupling facility (CF) due
  to BOTRSUPD,
  Feature Toggle:
  com.ibm.cics.cpsm.wlm.botrsupd.enabled={TRUE|false}
  V5.4/5.5/5.6: APAR PH14812. The default is true.
  
  
  The 'Region status server, bottom-tier parameter (BOTRSUPD)'
  topic will be updated to describe the new toggle.  A new section
  will be added:
  
  Disabling updates to the CF due to BOTRSUPD
  You can set the following feature toggle to disable updates to
  the Coupling Facility when the task load falls below the lower
  tier threshold.
  com.ibm.cics.cpsm.wlm.botrsupd.enabled=false
  The lowest possible setting for BOTRSUPD is 1%. Therefore,
  regions with a high MXT setting, which spend a significant
  amount of time operating below 1% of their declared capacity,
  might perform a high number of CF updates. With this feature
  toggle in effect, when the task load for a region falls within
  the BOTRSUPD range, no updates will be made to the CF. The task
  load value stored in the CF will remain zero until the first
  task load boundary defined by the UPDATERS parameter is reached.
  
  Note that if only a subset of target regions within a workload
  are run with com.ibm.cics.cpsm.wlm.botrsupd.enabled=false, then
  those regions may take a greater proportion of the workload.
  

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:

  UI70941 UI70942 UI70943

Modules/Macros

• DFHRSDM  DFHRSDUF DFHRSSR  DFHRSXM
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R100 PSY UI70943

     UP20/08/11 P F008

• R200 PSY UI70942

     UP20/08/11 P F008

• R300 PSY UI70941

     UP20/08/11 P F008

Fix is available

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