Re: os cache vs. db cache

I was wondering if anyone know what happens in UNIX (any flavour) if you
stored many databases under same filesystem? Is there any sort of filesystem
lock or something?

Thanks

--
LSC



On 7/9/07, Allen, Brandon <Brandon.Allen@xxxxxxxxxxx> wrote:


 I'd be curious to hear anyone's reasons for preferring OS cache to DB
cache.

It seems pretty clear cut to me that it is better to allow Oracle to
manage its own cache since it has much more knowledge available internally
to help predict which blocks are most likely to be needed again.  I've had
good results with CIO (Concurrent, a.k.a non-buffered, non-inode-locking
I/O) on AIX, but I did increase db_cache_size to make up for the lack of
filesystem buffering - in one case from 600M to 1500M, in another I just
used CIO from the beginning so there was no before/after comparison, but
performance has been excellent with CIO.  In the case where I switched from
regular, buffered I/O to CIO and increased db_cache_size from 600M to 1500M,
the performance of a fixed set of batch jobs improved from an average
runtime of 166 minutes to 129 minutes - so a 22% reduction in runtime, but
it's difficult to say how much of that improvement was from switching to CIO
and how much was just due to the increase in db_cache_size alone.

Here's a great paper specifically on AIX CIO for more info:
http://www-03.ibm.com/servers/aix/whitepapers/db_perf_aix.pdf

 ------------------------------
*From:* oracle-l-bounce@xxxxxxxxxxxxx [mailto:
oracle-l-bounce@xxxxxxxxxxxxx] *On Behalf Of *Robyn


Over the years, I've read differing opinions on balancing the os cache and
the database cache.

Privileged/Confidential Information may be contained in this message or
attachments hereto. Please advise immediately if you or your employer do not
consent to Internet email for messages of this kind. Opinions, conclusions
and other information in this message that do not relate to the official
business of this company shall be understood as neither given nor endorsed
by it.

Other related posts: