From: Jeff Lightner (jlightner@water.com)
Date: Fri Dec 03 2004 - 11:17:01 EST
Is there any value in increasing buffer cache for Oracle databases when
using EMC Symmetrix?
If so are there guidelines for how much to increase it?
PLEASE: Do not respond with dynamic vs. static kernel parameters or HOW to
increase it or thrashing concerns if it is increased as I am aware of these
things. The questions are aimed at understanding WHY increasing it would
be of value.
BACKGROUND:
Based on information gained at HP World some years back and later
reconfirmed in this forum for 11.0 we are reluctant to set system buffer
cache beyond 300 MB. This is because our understanding is that the caching
algorithm isn't efficient beyond that level (at least in 10 and 11.0 -
haven't heard about 11i). Also our understanding from our DBAs is that
Oracle recommends not using system buffer cache as it has its own caching
mechanism. On top of that the Symmetrix itself has its own cache.
Despite all of this it is being suggested by an EMC person that we increase
our buffer cache at the OS level. He believes this will allow us to hit the
"normal" 90% rcache level he would expect to see.
The 11.0 system is running Oracle 8x on vxfs filesystems built under Veritas
Volume Manager volumes.
TIA and I will summarize.
Jeffrey C. Lightner
Unix Systems Administrator
DS Waters of North America
678-486-3516
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