RE: os cache vs. db cache

Hi Robin,
I have got positive experience using  os cache when running OLTP (not DWH!) 
databases.
I believe it was a "special" case -> many concurrent sessions were accessing 
the same index (hot) blocks.
We have got many "cache buffer chains" latches, and they constituted ~ 20-25% 
of database resource usage (top5 wait
events as of STATSPACK reports). After  swithing on the os cache (HPUX 11.11, 
16 CPUs, Veritas Filesystem ), the "cache
buffer chains" issues vanisched.
So the overhead of double buffering was in this case offset by elimination of 
latch contention. 
Response time for all the critical queries halved.  
HTH. Milen 
 
P.S.   It was third party application, where creating storedoutlines after each 
application release was not fun at all
;( 
 

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Robyn
Sent: Monday, July 09, 2007 8:04 PM
To: oracle-l
Subject: os cache vs. db cache


Hello everyone,

Over the years, I've read differing opinions on balancing the os cache and the 
database cache.  Seems like I remember
there were some advocates for minimizing the os cache and maximizing the 
database cache to allow Oracle to better
determine which blocks should truly be cached and avoid necessary blocks being 
cached because they were in proximity to
hot data.  I also have heard opposite opinions. 

I'm specifically focused on performance for a data warehouse.  Has anyone 
tested performance with a minimized OS cache
and a maximized database cache?  If so, what were the results?  Does anyone 
have a really good paper or book on the
topic?  I'm trying to collect some information before I start discussions with 
the platforms guys. 

tia ... Robyn

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