Running with persistent sessions support

When you specify SNPS or MNPS for the PSTYPE system initialization parameter so that z/OS® Communications Server persistent sessions support is in use for a CICS® region, the time specified by the PSDINT system initialization parameter for the region determines how long the sessions are retained.

If a CICS, Communications Server, or z/OS failure occurs, if a connection to the Communications Server is reestablished within this time, CICS can use the retained sessions immediately; there is no need for network flows to rebind them.

Make sure that you set a nonzero value for the persistent sessions delay interval, so that sessions are retained. The default is zero, which means that persistent sessions support is available if you have specified SNPS or MNPS for PSTYPE, but it is not being exploited.

You can change the persistent sessions delay interval using the CEMT SET VTAM command, or the EXEC CICS SET VTAM command. The changed interval is not stored in the CICS global catalog, and therefore is not restored in an emergency restart.

Note: VTAM® is now the z/OS Communications Server.

During an emergency restart of CICS, CICS restores those sessions pending recovery from the CICS global catalog and the CICS system log to an in-session state. This process of persistent sessions recovery takes place when CICS opens its VTAM ACB. With multinode persistent sessions support, if the Communications Server or z/OS fails, sessions are restored when CICS reopens its VTAM ACB, either automatically by the COVR transaction, or by a CEMT or EXEC CICS SET VTAM OPEN command. Although sessions are recovered, any transactions inflight at the time of the failure are abended and not recovered.

When a terminal user enters data during persistent sessions recovery, CICS appears to hang. The screen that was displayed at the time of the failure remains on display until persistent sessions recovery is complete. You can use options on the TYPETERM and SESSIONS resource definitions for the CICS region to customize CICS so that either a successful recovery can be transparent to terminal users, or terminal users can be notified of the recovery, allowing them to take the appropriate actions.

If APPC sessions are active at the time of the CICS, Communications Server or z/OS failure, persistent sessions recovery appears to APPC partners as CICS hanging. The Communications Server saves requests issued by the APPC partner, and passes them to CICS when recovery is complete. When CICS reestablishes a connection with the Communications Server, recovery of terminal sessions is determined by the settings for the PSRECOVERY option of the CONNECTION resource definition and the RECOVOPTION option of the SESSIONS resource definition. You must set the PSRECOVERY option of the CONNECTION resource definition to the default value SYSDEFAULT for sessions to be recovered. The alternative, NONE, means that no sessions are recovered. If you have selected the appropriate recovery options and the APPC sessions are in the correct state, CICS performs an ISSUE ABEND to inform the partner that the current conversation has been abnormally ended.

If CICS has persistent verification defined, the sign-on is not active under persistent sessions until the first input is received by CICS from the terminal.

Defining z/OS Communications Server persistent sessions support describes the steps required to define persistent sessions support for a CICS region.