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Re: os cache vs. db cache

From: LS Cheng <>
Date: Mon, 9 Jul 2007 23:40:14 +0200
Message-ID: <>

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?



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 - 16:40:14 CDT

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