Shared Message Datasets

Shared Message Datasets:

Up to now shared message queues and their message data have been stored in structures that are built in the Coupling Facility.  These structures are defined with a fixed size, so that all the message queues assigned to a particular structure, are constrained by this size.  Once a CF structure is full, the reason code 2192 is issued. This code indicates that the storage medium for that queue is full. In IBM WMQ V7.1 new function mode, a new construct called a Shared Message Dataset has been added for preventing CF structures from filling up. The SMDS is a linear VSAM dataset much like a page-set for non-shared queues today, but is associated with a CF structure.

Implementation of Shared Message Datasets

Before implementing  a SMDS architecture all the queue managers in the queue sharing group should be having the OPMODE=(NEWFUNC ,710) set in the ZPARM. Once this has been set, and the queue managers have been restarted we can now allocate the Shared Message Datasets.

Each Queue Manager in the queue sharing group will have its own copy of the SMDS for a coupling facility structure.  This is designated by the use of an * in the DSGROUP parameter of the CFSTRUCT definition.