Limitation of concurrent threads
The number of tasks accessing the queue manager could also have an impact
on performance, particularly if there are other constraints, such as storage,
or there are a large number of tasks accessing a few queues. Symptoms of this
could be heavy I/O against one or more page sets, or poor response times from
tasks known to access the same queues.
There are three parameters specified in the CSQ6SYSP macro that control
the number of threads (see the WebSphere MQ for z/OS System Setup Guide for details). These are:
- IDFORE
- Specifies the number of TSO sessions that can connect to the queue manager
concurrently.
- IDBACK
- Specifies the number of batch tasks (excluding TSO tasks) that can connect
to the queue manager.
- CTHREAD
- Specifies the total number of threads that can connect to the queue
manager. This includes batch, TSO, IMS(TM), and CICS(R).
Notes:
- Each CICS region takes up nine of the threads specified here, plus one thread
for each task initiator (CKTI).
- The channel initiator makes a number of connections to the queue
manager that you must allow for when setting the CTHREAD system parameter. The number of connections is up to eight plus the combined value
of the queue manager parameters CHIADAPS and CHIDISPS. These values are
queue manager attributes and you can set them using the
ALTER QMGR command. See the WebSphere MQ Script (MQSC) Command Reference for more information.
- For IMS connections, the number of threads required is one for the control
region, and one for each dependent region connected to WebSphere MQ. For each IMS MPP
or IFP region that is defined to permit WebSphere MQ connections through either a
specific SSM=EXEC parameter or through the control region default, a thread
is created when the first application is scheduled in that region, regardless
of whether that application invokes any WebSphere MQ calls. The value you set for
CTHREAD should take account of this.
You can change the number of threads while a queue manager is running by
using the SET SYSTEM command.
In a CICS environment, you can use CICS MAXTASK to limit concurrent access.