[Info-vax] improve performance of /EXCLUDE

[David Froble]

mcleanjoh at gmail.com wrote:

> What difference do larger RMS buffers make to the search time?
> 
> I once wrote a 'copy' program (with an entry point to make it
> callable) that saw how much memory I had available (i.e. WSMAX less
> current allocation) and used a large chunk of that as the copy
> buffer.  I *think* it was faster than normal copy but it wasn't easy
> to check this because on the first run the file got cached on the SAN
> and read access fell quite a bit. A 'search' using a similar system
> might be very fast.

I don't think that you'll do better than reading whatever the disk 
cluster size is.  You're still limited by disk seeks and transfers.

Now, async read ahead with multiple buffers while working on already 
read data will give you a wall time boost.  If you're not waiting for a 
disk, then you won't get any faster than however long the CPU(s) take to 
do the in memory work.  Usually you'll be I/O bound.

That's a traditional perspective.  Today there are SANs and SSDs and 
such, which changes the rules ....

With today's multiple cores, if your software can use multiple cores, 
that can also change timing, but, the software can be more complex.