The SHOWCAT macro lets you get information about a component before its cluster or alternate index is opened. The program that is to issue BLDVRP can issue SHOWCAT on all the components to find out the sizes of control intervals, records, and keys. This information lets the program calculate values for the BUFFERS and KEYLEN parameters of BLDVRP.

A program need not be in supervisor state with protection key 0 - 7 to issue SHOWCAT, even though it must be in supervisor state and in protection key 0 - 7 to issue BLDVRP TYPE=GSR.

The SHOWCAT macro is described in z/OS DFSMS Macro Instructions for Data Sets.