Named counter servers

CICS provides a facility for generating unique sequence numbers for use by application programs in a Parallel Sysplex® environment. This facility is controlled by a named counter server, which maintains each sequence of numbers as a named counter.

Each time a sequence number is assigned, the corresponding named counter is incremented automatically. By default, the increment is 1, ensuring that the next request gets the next number in sequence. You can vary the increment when using the EXEC CICS GET command to request the next number.

There are various uses for this facility, such as obtaining a unique number for documents (for example, customer orders, invoices, and despatch notes), or for obtaining a block of numbers for allocating customer record numbers in a customer file.

In a single CICS region, there are various methods you can use to control the allocation of a unique number. For example, you could use the CICS common work area (CWA) to store a number that is updated by each application program that uses the number. The problem with the CWA method is that the CWA is unique to the CICS address space, and cannot be shared by other regions that are running the same application. A CICS shared data table could be used to provide such a service, but the CICS regions would all have to reside in the same MVS™ image. The named counter facility overcomes all the sharing difficulties presented by other methods by maintaining its named counters in the coupling facility, and providing access through a named counter server running in each MVS image in the sysplex. This ensures that all CICS regions throughout the Parallel Sysplex have access to the same named counters.

When you use a named counter server, each normal request (to assign the next counter value) only requires a single coupling facility access. This provides a significant improvement in performance compared to the use of files for this purpose. The named counter server also performs better than coupling facility data tables in this respect, because at least two coupling facility accesses are required to update a coupling facility data table. Depending on your hardware configuration, you should easily be able to make many thousands of named counter server requests each second.