Oracle-L: Re: mbrc (was: buffer cache

From: Boris Dali <boris_dali_at_yahoo.ca>
Date: Tue, 13 May 2003 14:20:34 -0800
Message-ID: <F001.00598310.20030513142034@fatcity.com>

Jonathan,

Jonathan Lewis <jonathan_at_jlcomp.demon.co.uk> wrote: >
> Points to note:
>
> Table size = 10600 - ish
>
> 99 * 128 =12672
> 680 * 16 = 10880
>
> So your 128 block reads were pretty
> successful reads, averaging about 107
> blocks each.
>

That's correct. In fact p3=126 for most of the 'db file scattered read' events (ranging from 5 to 128). But if it is successful and it does issue some 7 times less I/O reguests - why does it take longer to execute?

> Is it possible that you have a system
> striped as 128K per disk ? This might
> be consistent with the side-effects of
> contention when all parts of a 128 BLOCK
> read having to complete (making 8 discs
> busy) before the whole read is complete,
> when a 16 block read need only wait for
> one disc at a time.

Nope. No striping, in fact no raid at all. Plain JBOD. The whole table is on a single disk.

>
> Was this repeatable, and was there other
> activity in unrelated areas of the system
> at the time ?
>

Yes it was repeatable at the time I did the tests. There was some minor activity (not heavy on I/O), but I will try again latter on today.

>
> Regards
>
> Jonathan Lewis
> http://www.jlcomp.demon.co.uk
>
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> Jr
>
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Thanks a lot, Jonathan.

Boris Dali.

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Received on Tue May 13 2003 - 17:20:34 CDT

Re: mbrc (was: buffer cache - once again)