Pseudo WFI option for MPP regions in DB/DC and DCCTL environments

The pseudo WFI (pseudo wait-for-input) option allows an MPP region to remain scheduled until another input message appears. With pseudo WFI, unnecessary application program termination and rescheduling can be eliminated.

Normally, if an MPP region is scheduled for a transaction and no more messages for that transaction exist, the application program terminates. Frequently, another message appears for the same transaction after the program is terminated. Processor usage is increased because of unnecessary termination and rescheduling of that application program.

Pseudo WFI is specified with the PWFI= parameter on the MPP region startup procedure. When PWFI=Y is specified, the processing limit count is greater than 0, the PSB is not allocated with the dynamic PSB option (DOPT) and no more messages are queued for the current MODE=SNGL transaction, IMS checks for other work for the region to process. If no other work is available, the region waits until another input message appears. This is wait-for-input mode.

When the next input message is for the currently scheduled transaction, the message is returned to the application program with a status code of blank-blank.

When the next message is not for the currently scheduled transaction, termination and rescheduling occur.

In certain circumstances, regions that are in wait-for-input mode will be posted and a QC status code is returned to the application program. These circumstances include:
  • Commands that involve stopping, starting, locking, unlocking, or purging
  • Commands that involve assigning a database, region, transaction, or class
  • The UPDATE PGM START(REFRESH) command
    Note: The UPDATE PGM START(REFRESH) command is not supported for MPP regions where the program is loaded by the DFSMPLxx PROCLIB member.

    When application program changes are made in IMS.PGMLIB, you can issue the UPDATE PGM START(REFRESH) command to post the MPP PWFI regions so that a refreshed copy of the application program can be obtained when the program gets scheduled again. By using this command, you do not have to find all of the regions that the program is scheduled in and to stop those regions manually. The UPDATE PGM START(REFRESH) command is supported for programs scheduled in MPP PWFI regions that have the program scheduled in them and the program is not preloaded by the DFSMPLxx PROCLIB member, .

The following circumstances also cause similar problems:
  • An intent conflict scheduling failure might occur as a consequence of either a local or global load balancing algorithm decision. This causes all PWFI regions to be posted and QC status codes to be returned to the application programs.

    The global load balancing algorithm is a feature of Sysplex Serial Program Manager (SSPM).

  • A resource enters the OLC PREPARE phase. This causes all PWFI regions to be posted and a QC status code to be returned to the application programs.
  • A program or transaction is stopped as a consequence of a dependent region abend. This causes all PWFI regions to be posted and QC status codes to be returned to the application programs that belong to regions with stopped programs or transactions.

Regions that cannot be scheduled because of a lack of pool space can also post regions currently in pseudo WFI in an attempt to terminate them. This frees pool space so that the failing region can schedule.