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XZIQUE exit for managing intersystem queues
You can use the XZIQUE exit to control the number of queued requests for
sessions on intersystem links (allocate queues).
Note: There are several methods that you can use to control the length of
intersystem queues. For a description of the various methods, see the
CICS
Intercommunication Guide
.
The XZIQUE exit enables you detect queuing problems (bottlenecks) early. It
extends the function provided by the XISCONA global user exit (introduced in
CICS/ESA 3.3 and described on page 127), which is invoked only for function
shipping and DPL requests. XZIQUE is invoked for transaction routing,
asynchronous processing, and distributed transaction processing requests, as well
as for function shipping and DPL. Compared with XISCONA, it receives more
detailed information on which to base its decisions.
XZIQUE enables allocate requests to be queued or rejected, depending on the
length of the queue. It also allows a connection on which there is a bottleneck to be
terminated and then re-established.
Interaction with the XISCONA exit
There is no interaction between the XZIQUE and XISCONA global user exits. If you
enable both exits, XISCONA and XZIQUE could both be invoked for function
shipping and DPL requests, which is not recommended. You should ensure that
only one of these exits is enabled. Because of it provides more function and greater
flexibility, it is recommended that you use XZIQUE rather than XISCONA.
If you already have an XISCONA global user exit program, you could possibly
modify it for use at the XZIQUE exit point.
When the XZIQUE exit is invoked
The XZIQUE global user exit is invoked, if it is enabled, at the following times:
v Whenever CICS tries to acquire a session with a remote system and there is no
free session available. It is invoked whether or not you have specified the
QUEUELIMIT option on the CONNECTION definition, and whether or not the
limit has been exceeded. It is not invoked if the allocate request specifies
NOQUEUE or NOSUSPEND.
Requests for sessions can arise in a number of ways, such as explicit EXEC
CICS ALLOCATE commands issued by DTP programs, or by transaction routing
or function shipping requests.
v Whenever an allocate request succeeds in finding a free session, after the queue
on the connection has been purged by a previous invocation of the exit program.
In this case, your exit program can indicate that CICS is to continue processing
normally, resuming queuing when necessary.
Using an XZIQUE global user exit program
When the exit is enabled, your XZIQUE global user exit program is able to check
on the state of the allocate queue for a particular connection in the local system.
Information is passed to the exit program in a parameter list, that is structured to
provide data about non-specific allocate requests, or requests for specific
VTAM working-set module exits
Chapter 1. Global user exit programs 237
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