Everhart, Glenn
From:	Roy Omond [Roy.Omond@BlueBubble.Demon.co.uk]
Sent:	Tuesday, September 29, 1998 5:10 AM
To:	Info-VAX@Mvb.Saic.Com
Subject:	Re: VIOC Analysis
Hein RMS van den Heuvel wrote:

> VIOC can only help to ease the pain for excess reads.
> It has also a build in cut-off at 35 blocks.

Just wanted to add that knowing this fact can help overall performance(I've utilised this at several
contract sites).  If you *know* you're
definitely not going to access a file in the "near future", then the last
thing you want to do is to zonk the VIOC by pushing stuff out and
replacing it with blocks that have zero probability of being reused.
Example:  you've just finished working on a file and it's destined
for some archive place, then:

    $ Set RMS/Block="something bigger than 35"
    $ Copy File.ForArchive    $Archive:

This can make quite a difference in certain circumstances (though it's
difficult to quantify;  sometimes gut-feeling is scientific enough :-)

> To really speed things up, you may have to look higher up.
> Like WHY is the app reading the file over and over?
> Can you give it an index to just go for the records really needed?
> Or, HOW is the file being read? Using plain old RMS $GETs with no
> special settings? Try READ-AHEAD and more larger buffers
> Just try $SET RMS/BUF=8/BLOCK=32 or /BLOCK=120..
>  Just two files and multiple shared readers?  Tried GLOBAL BUFFERSs?
> (yes they can also be used for sequential files.)

As always, wise words from Hein.

Roy Omond
Blue Bubble Ltd.