Are enough sessions defined?

To help you determine whether you have enough sessions defined, you can check a number of peak fields that CICS® provides in the statistics report.

The peak fields are:
  1. Peak outstanding allocates (fields A14ESTAM and A20ESTAM) Total number of allocates (field A14ESTAS) Total specific allocate requests (field A20ESTAS).

    When reviewing the number of sessions for APPC modegroups, and the number of Peak outstanding allocates appears high in relation to the Total number of allocates, or the Total specific allocate requests within a statistics reporting period, it could indicate that the total number of sessions defined is too low.

  2. Peak contention winners (fields A14E2HWM and A20E2HWM) Peak contention losers (fields A14E1HWM and A20E1HWM)

    If the number of (Peak contention winners + Peak contention losers) equals the maximum number of sessions available (as defined in the SESSIONS definition), this indicates that, at some point in the statistics reporting period, all the sessions available were, potentially, in use. While these facts alone may not indicate a problem, if CICS also queued or rejected some allocate requests during the same period, the total number of sessions defined is too low.

  3. Failed allocates due to sessions in use (fields A14ESTAO and A20ESTAO)

    This value is incremented for allocates that are rejected with a SYSBUSY response because no sessions are immediately available (that is, for allocate requests with the NOSUSPEND or NOQUEUE option specified). This value is also incremented for allocates that are queued and then rejected with an AAL1 abend code; the AAL1 code indicates the allocate is rejected because no session became available within the specified deadlock timeout (DTIMOUT) time limit.

    If the number of Failed allocates due to sessions in use is high within a statistics reporting period, it indicates that not enough sessions were immediately available, or available within a reasonable time limit.

Action: Consider making more sessions available with which to satisfy the allocate requests. Enabling CICS to satisfy allocate requests without the need for queueing may lead to improved performance.

However, be aware that increasing the number of sessions available on the front end potentially increases the workload to the back end, and you should investigate whether this is likely to cause a problem.