[Info-vax] Raxco VMS Tuning Seminar Notes

[Neil Rieck]

On Nov 3, 1:43 pm, jls <notva... at yahoo.com> wrote:

>
[...snip...].
>

AFAIAC, the problem with the confusion around VMS tuning is due to the
fact that many concepts are spread across multiple VMS manuals. So
yesterday I was reading semi-unofficial VMS docs like "OpenVMS System
Management Guide" which also gives the impression that AWSA runs
independently every so often (like WATCHDOG or HITMAN). See topic
18.7.3.2 or click the following link:

http://books.google.ca/books?id=yn9RN2e32J4C&pg=PA421&lpg=PA421&dq=awsa+pfratl&source=bl&ots=Y4sWnsr8wm&sig=c60U2gj0hym3TJ_e7bhIq2zD6Ic&hl=en&ei=Md_TTLP6LNGbnwfCreHLBQ&sa=X&oi=book_result&ct=result&resnum=5&sqi=2&ved=0CCwQ6AEwBA

But this official document "VMS System Performance Management" (see
topic: 3.5.6 titled "Voluntary Decrementing")
http://h71000.www7.hp.com/doc/73final/6491/6491pro_003.html
discusses PFRATL in a context which has nothing to do with swapper
trimming but everything to do with the process limiting itself.
itself. So thanks for setting me straight.

###

Okay so what would a system look like with with AWSA-
Contraction(Reduction) disabled?
Well, if the system becomes short of memory then swapper trimming
would knock some/all processes who have borrowed memory over quota
back to quota. If the system is still short of memory then some procs
would be reduced even further to SWPOUTPGCNT (unless it was manually
set higher) prior to swapping out.

So I think it is better to have processes reducing their own memory
requirements (acting like good citizens in the system) provided it
doesn't invoke too much thrashing (hard or soft).

How could you reduce AWSA thrashing?
1) Increase AWSMIN so you don't surrender below a certain value
2) Reduce the size of WSDEC to a value below WSINC (the default SYSGEN
values are the other way around). This would result in process being
able to get more memory when it was required but surrendering fewer
pages when required. Don't worry, if you get this wrong then then you
can always fall back on swapper trimming
3) Make AWSTIME some small multiple of QUANTUM. (don't make it too
high as this would also affect AWSA-Expansion)

But all of this is moot if you've got plenty of memory like I do on my
AS-DS20e with 3 GB. It is a different story on my AS-2100 which only
has 128 MB

NSR