The size of the structure will be installation-specific in most cases. Therefore, you should provide a formula, a chart, or other “rule of thumb” to assist in calculating an initial structure size. You might also provide some methods of tuning the structure size after it is in use by your application.

The Structure Computation Service (IXLCSP) can be used to calculate the approximate structure size for cache, list, and lock structures. The service accepts as input the structure attributes and object counts and returns the structure size appropriate to the CFLEVEL of the target facility. The input parameters passed as input to IXLCSP map directly to the parameters specified on IXLCONN.

PR/SM Planning Guide provides a set of formulas that you can use as a first step in determining an approximate structure size. There are two formulas — one for cache and one for list (a lock structure is considered to be a list structure). The values that are inserted into these formulas come primarily from the values you specify on your IXLCONN invocation to connect to the structure. If you plan to provide a formula to determine a structure's size, you could use your IXLCONN parameters to simplify the calculation. The installation then would only need to provide the installation-specific input to your simplified formula.

For coupling facilities at CFLEVEL=8 and higher, the formulas provided in PR/SM Planning Guide have not been updated. Instead, it is recommended that you use the IXLCSP macro to estimate the structure storage requirement.