Controlling sessions with the SET MODENAME commands

The SET MODENAME commands can be used to control the sessions within the modegroups associated with an APPC connection, without releasing or reacquiring the connection. The processes executed to accomplish this are:

The algorithms used by CICS® to negotiate with the partner the numbers of sessions to be made available are complex, and the numbers of sessions actually acquired may not match your expectation. The outcome can depend on the following:

Modegroups can normally be controlled with the few simple commands described in Table 8.

Table 8. SET MODENAME commands
Command Effect
SET MODENAME ACQUIRED Acquires all negotiated contention-winner sessions.
SET MODENAME CLOSED Negotiates with the partner to reduce the available number of sessions to zero, releases the sessions, and prevents any attempt by the partner to negotiate or activate any sessions in the modegroup. Only the system issuing the command can subsequently increase the session count.

Queued session requests are honored before sessions are unbound.

SET MODENAME AVAIL(maximum) ACQUIRED If this command is issued when the modegroup is closed, the sessions are negotiated as if the connection had been newly acquired, and the contention-winner sessions are acquired. It can also be used to rebind sessions that have been lost due to errors that have caused CICS to place sessions out of service.

Command scope and restrictions

User modegroups, which are built from CEDA DEFINE SESSIONS (or equivalent macro) definitions, can be modified by using the SET MODENAME command or by overtyping the INQUIRE MODENAME display data.

The SNASVCMG modegroup is built from the CONNECTION definition and any attempts to modify its status with a SET MODENAME command, or by overtyping the INQUIRE MODENAME display data, are suppressed. It is controlled by the SET CONNECTION command, or by overtyping the INQUIRE CONNECTION display data, which also affects associated user modegroups.

CEMT INQUIRE NETNAME, where the netname is the applid of the partner system, displays the status of all sessions associated with that connection, and can be useful in error diagnosis. Any attempt to alter the status of these sessions by overtyping, is suppressed.

You must use the SET|INQ CONNECTION|MODENAME to manage the status of user sessions and to control negotiation with remote systems.

A change to an APPC connection or modegroup can be requested by an operator issuing CEMT SET commands or by an application program issuing EXEC CICS SET commands. It is possible to issue one of these SET commands while a previous, perhaps contradictory, SET command is still in progress. This is particularly likely to occur in systems configured with large numbers of parallel sessions, in which the status of many sessions may be affected by an individual change to a connection or modegroup. Such overlapping SET commands can produce unpredictable results. You should therefore ensure that previously issued SET commands have fully completed before issuing the next SET command.

A similar situation can occur at startup if a SET CONNECTION or SET MODEGROUP command is issued while sessions are autoconnecting. You should therefore also ensure that all sessions have finished autoconnecting before issuing such a SET command.

Related concepts
General information about managing APPC links
Related tasks
Defining APPC links
Acquiring a connection
Releasing the connection
Related reference
Summary of APPC link management
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