From: Ayson, Alison {Info~Palo Alto} (ALISON.AYSON@ROCHE.COM)
Date: Thu Sep 05 2002 - 21:08:34 EDT
I have an N-class server (HP-UX 11.0) that runs Oracle 8.1.7 as its main
application. The system has 4 gigs of physical RAM. We are using dynamic
buffer caching and have db_max_pct set to 50%. I have to admit that I
didn't realize that the value was this high, and I have no idea why it was
decided to set it so high. These servers were built by the HP Integration
Center based on recommendations from a consultant (who's now gone).
The DBA's tried to install a third Oracle instance and received an "out of
memory" error. When I bring up glance and run the memory report I can see
that Buffer Cache is set to 2.0 gigs and Free Memory is around 300 megs.
The database was originally set to use much more memory (I believe around
500 megs), the DBAs had to reduce some SGA parameters to get the database
installed.
Now here's where I have to ask a stupid question. Is the buffer cache
dynamic in that it can be reduced (dynamically) if a process needs more
memory (such as an Oracle database), or is the Oracle install failing
because of this high buffer cache? (Basically is Oracle not allowed to
"steal" some of the memory from buffer cache...once it's allocated then you
are "screwed"..so to speak).
I've tried to search through the archives first and read up on bufpages,
etc. But I've never been much of a kernel parameter guru. I start reading
the help pages and my eyes start glazing over. I'd almost rather staple my
head to my cubicle.
We have some large fileysystems (the largest being 194 gigs). Our storage
is all provided by an EMC 8430 (8 gig hyper drives) with huge amounts of
cache.
Could the large buffer cache be the problem here? Why does it need to be so
high? Is that because of the large filesystems (and for the EMC)???
-- Alison Ayson
Roche Bioscience
Palo Alto, CA
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