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