Earlier today Jeff Milolai noted:
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We have been seeing impedes on our 989/650 .....
So we are escalated with HP now, and they responded
that we should enable DSEM and PREFETCH on our
databases. I am sorry, I just don't buy this. Why
enable an option we never had on in the first place?

Well anyway, does anyone have these options enabled?
I think it might be something I want to look into.
We are an extremely large MACS shop 1300+ users and
very large databases.
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We have had both DSEM and PREFETCH enabled on our
production database on our 959-400 for a long time
now;  at least a couple years if not longer, I think.
No problems at our site; and no outstanding problems
with either of these options anywhere AFAIK (which
of course doesn't guarantee there are no problems).

The August 1997 and later versions of the TurboIMAGE
DBMS Reference Manual have a good discussion of DSEM;
and a short description of PREFETCH.  PREFETCH is
covered mostly under "Coordinating Additions to a
Database" and similar for "Deletions" in Chapter 4.

There is just one caution listed in the manual for
enabling PREFETCH:  Be sure you have "Adequate CPU
and memory resources available on your system". Just
what constitutes "adequate" and how to make that
judgement is not defined;  I guess it's left as a
YMMV exercise to the reader.  FWIW, our 959 has 1.792
GB memory, and during routine daily operations (backup
or VSTORE not in process) our memory page fault and
Disc I/O rates per second are usually down in the
noise:  Less than 10 per second for disc I/O and less
than 5 per second for page faults is common.  Of
course we normally have less than 100 concurrent Jobs
and Sessions; our peak was somewhere around 120.  So
clearly compared to 1300+ users we are tiny...

Ken Sletten
SIGImage/SQL Chair

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