CICS Named Counter List Structure Help

CICS provides a facility for generating unique sequence numbers for use by application programs in a Parallel Sysplex environment.  This facility is provided by a named counter server, which generates each sequence of numbers using a named counter (where the counter name is an identifier of up to 16 characters).  Each time a sequence number is assigned, the corresponding named counter is incremented automatically.

A named counter is stored in a named counter pool, which resides in a list structure in a coupling facility.  The list structure name is of the form DFHNCLS_ poolname .  You can create different pools to suit your needs, for example if different sets of counters have different security requirements.  You could for example create a pool for use by production CICS regions called DFHNCPRD and others for test and development regions called DFHNCTST and DFHNCDEV.

A named counter pool name can be any valid identifier of up to 8 characters, but by convention pool names should normally be of the form DFHNCxxx. The default named counter options table assumes that when an application specifies a pool selector of this form it is referring to that physical named counter pool.  Any other pool selector for which there is no specific option table entry is mapped to the default named counter pool for the current region, or to the standard default pool name DFHNC001 if there is no specific default set for the current region.  This means that different applications can use their own logical pool names to refer to their named counters, but the counters will normally be stored in the default pool unless the installation specifically adds an option table entry to map that logical pool name to a different physical pool.

The structure size required for a named counter pool depends on the number of different named counters you need.  The minimum size of 256KB should be enough for most needs, as it holds hundreds of counters, but you can if necessary allocate a larger structure which can hold many thousands of counters, using this tool to calculate the required structure size.

This calculation determines the size of a structure which would be sufficiently large to contain at least the exact specified number of counters. However, for practical operation a reasonable proportion of free space must be available, not only to minimize the risk of the structure becoming totally full but also in order to avoid triggering low space warning messages.  The maximum normal usage should therefore aim to be not more than about 75% of the structure size.  When you have estimated the maximum number of counters that you will require, you should increase that number by about a third to allow for some free space when specifying the number of counters to be used for the space calculation.

Number of counters

Number of counters for which space is to be allocated in the named counter pool structure.