You must tell window services whether you intend to reference the
blocks of an object sequentially or randomly. An intention to access
randomly tells window services to transfer one block (4096 bytes)
of data into the window at a time. An intention to access sequentially
tells window services to transfer more than one block into your window
at one time. The performance gain is in having blocks of data already
in central storage at the time the program needs to reference them.
You specify the intent on either CSRVIEW or CSREVW, two services that
differ on how to specify sequential access.
To specify the reference pattern on CSRVIEW, supply a value of
SEQ or RANDOM for usage.
To specify the reference pattern on CSREVW, supply a number from
0 through 255 for pfcount. pfcount represents
the number of blocks window services will bring into the window, in
addition to the one that it always brings in.
Note that window services brings in multiple pages differently
depending on whether your object is permanent or temporary and whether
the system has moved pages of your data from central storage to make
those pages of central available for other programs. The rule is that
SEQ on CSRVIEW and
pfcount on CSREVW apply
to:
- A permanent object when movement is from
the object on DASD to central storage
- A temporary object when your program has
scrolled the data out and references it again.
SEQ and pfcount do not apply after the
system has moved data (either changed or unchanged) to auxiliary or
expanded storage, and your program again references it, requiring
the system to bring the data back to central storage.
End the view whether established with CSRVIEW or CSREVW, with CSRVIEW
END.