From: "Stephen C. Tweedie" <sct@redhat.com>
To: pamvdam@ramoth.xs4all.nl
Cc: Fernando Dammous <ferdam@internetcom.com.br>,
"Stephen C. Tweedie" <sct@redhat.com>,
Linux LVM msede <linux-lvm@msede.com>
Subject: Re: [linux-lvm] LVM, raw-io, devfs
Date: Mon, 4 Oct 1999 11:43:27 +0100 (BST) [thread overview]
Message-ID: <14328.33999.21844.718869@dukat.scot.redhat.com> (raw)
In-Reply-To: <19991003075644.A5224@ladystrange.bluehorizon.nl>
Hi,
On Sun, 3 Oct 1999 07:56:44 +0200, pamvdam@ramoth.xs4all.nl said:
> Oracle has always been using filesystems for it's datastorage. Only for
> the parrallel server configuration they demand RAW IO. Like Sybase 11.9.x
> under Linux it probably uses some O_SYNC flag to write to log, so the
> write call only returns when the data has been really written to the
> physical device. I don't think you'll see a performance enhancement when
> using Oracle and RAW/IO. There's even a chance, due to the fact you mis
> the buffer cache optimisations, that you'll see a performance
> degradation.
It depends. Raw IO uses less CPU --- much less in some cases. It also
avoids polluting memory with extra copies of data in the buffer cache.
As a result, just measuring the pure disk bandwidth of raw IO versus
buffered IO does not tell you the whole story about performance: you
really need to measure the application's performance itself, including
the effect of CPU and memory pressure.
--Stephen
next prev parent reply other threads:[~1999-10-04 10:43 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-10-01 2:48 [linux-lvm] LVM, raw-io, devfs Fernando Dammous
1999-10-01 12:40 ` Adrien Farkas
1999-10-01 16:38 ` Stephen C. Tweedie
1999-10-01 18:39 ` Drew Smith
1999-10-01 19:15 ` Luca Berra
1999-10-02 15:01 ` Stephen C. Tweedie
1999-10-02 15:53 ` Eric Smith
1999-10-03 7:43 ` Harald Milz
1999-10-02 17:08 ` Fernando Dammous
1999-10-03 5:56 ` pamvdam
1999-10-04 10:43 ` Stephen C. Tweedie [this message]
1999-10-04 11:03 ` pamvdam
1999-10-03 10:14 ` Adrien Farkas
1999-10-03 17:23 ` Fernando Dammous
1999-10-04 9:28 ` Adrien Farkas
1999-10-04 10:44 ` Stephen C. Tweedie
1999-10-03 13:06 Daniel Whicker
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