IBM SC34-7012-01 Recovery with Vtam persistent sessions, Running with persistent sessions support

Recovery with VTAM persistent sessions

With VTAM persistent sessions support, if CICS fails or undergoes immediate shutdown (by means of a PERFORM SHUTDOWN IMMEDIATE command), VTAM holds the CICS LU-LU sessions in recovery-pending state, and they can be recovered during startup by a newly starting CICS region. With multinode persistent sessions support, sessions can also be recovered if VTAM or z/OS® fails in a sysplex.

The CICS system initialization parameter PSTYPE specifies the type of persistent sessions support for a CICS region:

SNPS, single-node persistent sessions

Persistent sessions support is available, so that VTAM sessions can be

recovered after a CICS failure and restart. This setting is the default.

MNPS, multinode persistent sessions

In addition to the SNPS support, VTAM sessions can also be recovered

after a VTAM or z/OS failure in a sysplex.

NOPS, no persistent sessions

Persistent sessions support is not required for the CICS region. For

example, a CICS region that is used only for development or testing might

not require persistent sessions.

For single-node persistent sessions support, you require VTAM V3.4.1 or later,

which supports persistent LU-LU sessions. CICS Transaction Server for z/OS,

Version 4 Release 1 functions with releases of VTAM earlier than V3.4.1, but in the

earlier releases sessions are not retained in a bound state if CICS fails. For

multinode persistent sessions support, you require VTAM V4.R4 or later, and

VTAM must be in a Parallel Sysplex® with a coupling facility. The VTAM Network

Implementation Guide explains the exact VTAM configuration requirements for

multinode persistent sessions support.

CICS support of persistent sessions includes the support of all LU-LU sessions,

except LU0 pipeline and LU6.1 sessions. With multinode persistent sessions

support, if VTAM or z/OS fails, LU62 synclevel 1 sessions are restored, but LU62

synclevel 2 sessions are not restored.

Running with persistent sessions support

When you specify SNPS or MNPS for the PSTYPE system initialization parameter so that VTAM 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, VTAM, or z/OS failure occurs, if a connection to VTAM 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.

38CICS TS for z/OS 4.1: Recovery and Restart Guide