Resource name uniqueness

IMS ensures that a resource name is active only once in the IMSplex at any particular time. IMS systems within the IMSplex cannot activate the same resource at the same time. The IMSplex automatically enforces resource name uniqueness only when Resource Manager (RM) is active and a resource structure is defined in the coupling facility.

When a resource is active, it is owned by one IMS in the IMSplex. No other IMS can activate the same resource until it becomes inactive on the owning IMS.

Name uniqueness is enforced only for VTAM® LTERMs, VTAM single-session nodes, user IDs, and users. IMS no longer supports BTAM terminals.

Name uniqueness is enforced for user IDs only if SGN is not M. User ID name uniqueness enforcement is not automatic. However, name uniqueness for VTAM LTERMs, VTAM single-session nodes, and users is automatically enforced if you have RM and a resource structure defined.

For ISC terminals, if the option for disabling resource sharing in the IMSplex is on in the DFSINTX0 user exit routine, resource name uniqueness is not enforced for static LU 6.1 sessions. Name uniqueness is not enforced for ISC TCP/IP terminals (static and dynamic).

Disabling enforcement of resource name uniqueness

You can disable the enforcement of resource name uniqueness, and TM resource sharing in general, by specifying STM=NO in the DFSDCxxx PROCLIB member data set.

Related reading: See Transaction Manager resources for more detailed information about how and why IMS enforces name uniqueness for particular resources.