Defining the reference pattern (REFPAT)

The REFPAT macro allows a program to define a reference pattern for a specified area that the program is about to reference. Additionally, the program specifies how much data it wants the system to attempt to bring into central storage on a page fault. The system honors the request according to the availability of central storage. By bringing in more data at a time, the system takes fewer page faults; fewer page faults means possible improvement in performance.

Programs that benefit from REFPAT are those that reference amounts of data that are greater than one megabyte. The program should reference the data in a sequential manner, either forward or backward. In addition, if the program "skips over" certain areas, and these areas are of uniform size and are repeated at regular intervals, REFPAT might provide additional performance improvement. Although REFPAT affects movement of pages from auxiliary and expanded storage, the greatest gain is for movement of pages from auxiliary storage.

There are two REFPAT services:

REFPAT INSTALL identifies the data area and the reference pattern, and specifies the number of bytes that the system is to try to bring into central storage at one time. These activities are called "defining the reference pattern".
REFPAT REMOVE removes the definition; it tells the system that the program has stopped using the reference pattern for the specified data area.

A program might have a number of different ways of referencing a particular area. In this case, the program can issue multiple pairs of REFPAT INSTALL and REFPAT REMOVE macros for that area.

Each pattern, as defined on REFPAT INSTALL, is associated with the task that represents the caller. A task can have up to 100 reference patterns defined for multiple data areas at one time, but cannot have more than one pattern defined for the same area. Other tasks can specify a different reference pattern for the same data area. REFPAT REMOVE removes the association between the pattern and the task.

The data area can be in the primary address space or in a data space owned by a task that was dispatched in the primary address space. If the data area is in a data space, identify the data space through its STOKEN. You received the STOKEN either from DSPSERV or from another program.

Although REFPAT can be used for data structures other than arrays, for simplicity, examples in this chapter use REFPAT for an array or part of an array.

Reference pattern services for high-level language (HLL) and assembler language programs provide function similar to what REFPAT offers. For information about these services, see z/OS MVS Programming: Callable Services for High-Level Languages.