Defining the reference pattern

This information assumes that your program's reference pattern meets the basic requirement of consistent direction. Figure 1 identifies tw o reference patterns that characterize most of the reference patterns that REFPAT applies to. The marks on the line indicate referenced elements.

How you define the reference pattern depends on whether your program's reference pattern is like Pattern #1 or Pattern #2.

• With Pattern #1 where no uniform gap exists, the program uses every element, every other element, or at least most elements on each page of array data. No definable gap exists. Do not use REFPAT if the reference pattern is irregular and includes skipping over many areas larger than a page.
  • The UNITSIZE parameter alone identifies the reference pattern. (Either omit the GAP parameter or take the default, GAP=0.) UNITSIZE indicates the number of bytes you want the system to use as a reference unit. Look at logical groupings of bytes, such as one row, a number of rows, or one element, if the elements are large in size. Or, you might choose to divide up the total area, bringing in all the data on a certain number of page faults.
  • The UNITS parameter tells the system how many reference units to try to bring in on a page fault. For a reference pattern that begins on a page boundary and has no gap, the total number of bytes the system tries to bring into central storage at a time is the value on UNITSIZE times the number on UNITS, rounded up to the nearest multiple of 4096. See Choosing the number of bytes on a page fault for more information on how to choose the total number of bytes.
• With Pattern #2 where a uniform gap exists, you tell the system the sizes of reference units and gaps.
  • UNITSIZE and GAP parameters identify the reference pattern. Pattern #2 in Figure 1 includes a reference unit of 20 bytes and a gap of 5000 bytes. Because the gap is greater than 4095, some pages of the array might not come into central storage.
  • The UNITS parameter tells the system how many reference units to try to bring into central storage at a time. What pages does the system bring in when a gap exists? can help you understand how many bytes come into central storage at one time.