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Re: os cache vs. db cache

From: Robyn <>
Date: Mon, 9 Jul 2007 17:34:15 -0400
Message-ID: <>

Thank you Mark and Brandon,

This is the kind of information I'm looking for; I've read Steve's stuff but it's been a while and the AIX paper is new to me. I *think* we need to make some changes in our approach, but right now, I just want to gather and study as much information on the different options and approaches as possible.

So, if anyone has additional links, documents or experiences, I'd appreciate the input.

thank you ... Robyn

On 7/9/07, Allen, Brandon <> 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:
> ------------------------------
> *From:* [mailto:
>] *On Behalf Of *Robyn
> Over the years, I've read differing opinions on balancing the os cache and
> the database cache.
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Received on Mon Jul 09 2007 - 16:34:15 CDT

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