CICS Transaction Gateway V5 The WebSphere ... - IBM Redbooks

156 CICS Transaction Gateway V5
EXCI pipe limitations
In CICS TS V1.3 and later, a single z/OS address space is limited (by the IRC
code) to only being able to allocate up to 100 EXCI pipes in total, to all attached
CICS regions. In contrast, maximum pipe usage in a CICS region is limited only
by the number of sessions defined in the CICS MRO SESSIONS definition,
which can be up to 999.
The following rules apply to the use of the EXCI by the CICS TG V5.0.0, and
apply equally to worker threads within the Gateway daemon or to threads within
WebSphere Application Server using the CICS TG local protocol.
► Each thread that services an ECI request will allocate an EXCI pipe. This pipe
remains allocated until either the thread is terminated, or the CICS MRO
connection is closed.
► Such pipes will be re-used by subsequent requests to the same worker
thread, but pipes are not shared across different worker threads.
► If a worker thread connects to multiple CICS regions, then multiple EXCI
pipes will be permanently allocated from the specific thread to these CICS
regions.
If the CICS TG tries to allocate more pipes than there are available CICS
sessions defined, the EXCI Open_Pipe call will fail with a RETRYABLE response,
and a reason code 202. The ECI application will receive a return code -16
(ECI_ERR_RESOURCE_SHORTAGE) and the EXCI User replaceable module
(DFHXCURM) will be invoked. In this instance you should consider configuring
the RECEIVECOUNT parameter in the CICS SESSIONS definition to be at least
100.
If the number of EXCI pipes in use exceeds 100, the 101st EXCI Allocate_Pipe
call will fail with a SYSTEM_ERROR response, and a reason code 608. The ECI
application will receive a return code -9 (ECI_ERR_SYSTEM_ERROR). Since
this means a limitation in the sending address space has been reached, you
should consider reducing the number of threads (that is, maxworker in the
Gateway daemon) to be less than or equal to 100/(number of attached CICS
regions).