Date: Tue, 11 Sep 2007 18:49:41 -0500
From: Decibel! <decibel@decibel.org>
To: Gregory Stark <stark@enterprisedb.com>
Cc: Jean-David Beyer <jeandavid8@verizon.net>,
 pgsql-performance@postgresql.org
Subject: Re: random_page_costs - are defaults of 4.0 realistic for SCSI RAID 1
Message-ID: <20070911234941.GN38801@decibel.org>
References: <C30B1716.4236C%llonergan@greenplum.com>
	<87lkbdlkxw.fsf@oxford.xeocode.com> <46E676D6.70807@verizon.net>
	<87zlzt9ifw.fsf@oxford.xeocode.com> <46E6E338.5050403@verizon.net>
	<20070911213105.GF38801@decibel.org>
	<87r6l4ajqh.fsf@oxford.xeocode.com>
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On Wed, Sep 12, 2007 at 12:02:46AM +0100, Gregory Stark wrote:
> "Decibel!" <decibel@decibel.org> writes:
>=20
> > On Tue, Sep 11, 2007 at 02:49:28PM -0400, Jean-David Beyer wrote:
> >> It is tricky for me to find a big enough file to test. I tried one of =
the
> >
> > dd if=3D/dev/zero of=3Dbigfile bs=3D8192 count=3D1000000
>=20
> On linux another useful trick is:
>=20
> echo 1 > /proc/sys/vm/drop_caches

The following C code should have similar effect...


/*
 * $Id: clearmem.c,v 1.1 2003/06/29 20:41:33 decibel Exp $
 *
 * Utility to clear out a chunk of memory and zero it. Useful for flushing =
disk buffers
 */

int main(int argc, char *argv[]) {
    if (!calloc(atoi(argv[1]), 1024*1024)) { printf("Error allocating memor=
y.\n"); }
}
--=20
Decibel!, aka Jim Nasby                        decibel@decibel.org
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)

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