From:	HENRY::IN%"MACALLSTR%vax1.physics.oxford.ac.uk%cs.ucl.ac.uk%sri-kl.ARPA%relay.cs.net@rca.com" 21-MAR-1987 18:42
To:	INFO-VAX <INFO-VAX%sri-kl.arpa@cs.ucl.ac.uk>
Subj:	VMS tuning.

Before anyone starts hacking/tweaking their SYSGEN parameters, my advice is
  DON'T - until you know your workload.
Let AUTOGEN give you the first 'stab' at setting SYSGEN parameters. Check
  through them to ensure that they're realistic for your system. Some packages
  ( networking, databases, etc ) may require ( and will usually recommend in
  the documentation ) some parameters to be increased - SYSGEN won't know about
  that.
Run all classes of the MONITOR utility ( + DISKS class ) over a period of time
  to discover what your 'typical' system demands are. There's a procedure in
  SYS$EXAMPLES which will do this for those new to VMS and will provide daily
  summaries. Old hands can benefit from this too.
Look for excessively high/low counts. Meaning of 'high/low' depends on processor
  type, disk configuration,etc. 
MONI xxx/current or SHOW SYS are quick ways of finding processes with high
  paging and I/O rates. Try to find out why the rates are high. You may be
  short of memory but, on the other hand, the process may simply be performing
  a lot of I/O.
Also check interactive response at the terminal, turn-round times for various
  activities,etc. Do they meet with your expectations? Are your expectations
  realistic? (You can't expect the same turnround on a micro-VAX for a CPU
  bound task as on an 8700! More powerful processors can also handle more I/O
  processing - but, remember, if all I/O is to/from one disk device, you may
  be limited by the speed of the device.)
How you arrange the memory use SYSGEN parameters ( WSMAX,etc ) and AUTHORIZE
  settings for WSQUOTA,etc depends on your job mix. For example, consider
  three types of system.
  (1) All users run interactively, at the same priority, and are generally
      CPU bound.
  (2) Users run interactively at one priority, batch jobs run at a lower
      priority. During the day there is almost no CPU time available to
      batch jobs.
  (3) Users run interactively at one priority, batch jobs at a lower priority
      but there are short lulls every ten minutes or so in the interactive use
      when batch jobs can use some CPU time. 
The settings of the SYSGEN parameters re: swapping/paging will be quite different
 for each case. The actual values will depend on how much free memory you have
 and how much physical memory a particular program requires. This last remark
 is very important. Each program has a 'critical working set size' below which
 it will page like mad and above which paging will occur at normal rates. You
 ought to check that high paging rates aren't due to this. You could waste a
 great deal of effort in tuning if this is the cause of high paging rates. Get
 to know your work load and monitor jobs which have high paging rates to ensure
 that working set sizes are adequate and also to check for bad program design,etc.

Reading the VMS Tuning manual explains the major aspects of tuning. I'd also
 recommend reading the SYSGEN parameter explanations in the SYSGEN manual so
 that you have some understanding of the effects of adjustments and, perhaps,
 to suggest to you other ways in which you might tune your particular system.

If you do make adjustments change only ONE thing at a time ( or one set of
 related parameters ). If you become too deeply immersed in tuning you'll
 never be satisfied - quit when you're nearly there; don't wait until you
 arrive - it'll never happen!

John