Michael Raithel <RAITHEM@WESTAT.COM> replied [in small part]:
> Richard, that is _MOST_ strange behavior, indeed! I would _LOVE_ to
> what operating system you are running this SAS application on.
> . . . .
> From what you describe, it is almost as if SAS is "reclaiming" the
> buffers from your previous DATA steps.
> . . . .
I was wondering the same thing myself, Mikeeeeee. It seems to me that
there is another possibility. The OP may be using caching controllers
for his hard drives, and the information may still be cached in the RAM
of the controller so that the OS is handed the info without having to
go hunt on the drive again.
But (if this wild, unsubstantiated speculation is true) this means that
early DATA _NULL_ to get the info into the controller cache won't help
when more work is done later, obliterating the controller cache with new
data from different drive sectors. This leads to a logical test. The
can do the same test as before, but adding a fast read of, say, the
2 Megs of the file in between the early indexing and the second
We might see the time required to do the second index suddenly jump back
up to what we would normally expect.
David Cassell, CSC
Senior computing specialist