Managing queues for intersystems sessions
When intersystems links are added to the system there is the possibility that they cannot respond adequately to transaction requests because the remote system is performing badly.
The poor performance can be due either to a long-term condition, such as lack of resource or overloading, or a temporary situation such as a memory dump being taken. In any case there is the danger that the problem can cause a long queue to form in the requesting system.
- Protection of the requesting system from using too many resources while transactions queue for the use of the intersystems sessions.
- Detection of problems in remote systems. CICS can issue messages to indicate a problem on an intersystems connection and the parameters control the criteria that are used to determine when a problem exists, or has gone away.
- The QUEUELIMIT and MAXQTIME parameters on the connection resource definition.
The QUEUELIMIT parameter limits the number of transactions which can be queued in allocate processing waiting for a session to become free. Any transactions which try to join a queue already at its limit are rejected.
The MAXQTIME parameter is a control on the wait time of queued allocate requests that are waiting for free sessions on a connection that appears to be unresponsive. If the rate of processing of the queue indicates that a new allocate will take longer than the specified time to reach the head of the queue, the whole queue is purged.
- The XZIQUE user exit, which is given control when an allocate request is about to be queued, or the first time it succeeds after a suspected problem. The XZIQUE exit can control the queue or you can use it to add more sophisticated controls of your own.
Both mechanisms produce the same effect on the application program which issued the allocate; a SYSIDERR condition is returned. Return codes are also provided to the dynamic routing program to indicate the state of the queue of allocate requests.
XZIQUE exit for managing MRO and APPC intersystem queues gives programming information about the XZIQUE exit and its relationship with the rest of CICS, including application programs and the dynamic routing program.