Queue server REGION parameter

The queue server REGION parameter JCL needs to specify at least enough virtual storage for the specified number of buffers plus the storage used to process queue requests.

Each buffer occupies a little more than 32K bytes, and each connected CICS® region can have up to ten queue requests active at a time, each using 5K to 10K bytes, so to be safe the REGION size should allow at least 32K per buffer and 100K for each connected CICS region, plus a margin of about 10% for other storage areas.

During server initialization, the server acquires all of the available storage above the 16M line, as determined by the REGION size, then releases 5% of it for use by operating system services. It also acquires 5% of the free storage below the line for use in routines which require 24-bit addressable storage, for example sequential file read and write routines.

After server initialization, AXM page allocation services are used to manage server region storage. Server statistics indicate how much storage is allocated and used within the storage areas above and below the 16M line, which are called AXMPGANY and AXMPGLOW in the statistics.

If a task in the server region or a cross-memory request runs out of storage, this is likely to result in AXM terminating that task or request using a simulated abend with system completion code 80A to indicate a GETMAIN failure. Although the server can usually continue processing other requests in this case, running out of storage in a critical routine can cause the server to terminate, so it is best to ensure that the REGION size is large enough to eliminate the risk.