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Message-ID: <b41c75520510110754g534d9fa8u@mail.gmail.com>
Date: Tue, 11 Oct 2005 16:54:31 +0200
From: Claus Guttesen <kometen@gmail.com>
To: Sven Willenberger <sven@dmv.com>
Subject: effective cache size on FreeBSD (WAS: Performance on SUSE w/
 reiserfs)
Cc: Jon Brisbin <jon.brisbin@npcinternational.com>,
	pgsql-performance@postgresql.org
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> > I have a postgresql 7.4.8-server with 4 GB ram.
> > #effective_cache_size =3D 1000    # typically 8KB each
> >
> > This is computed by sysctl -n vfs.hibufspace / 8192 (on FreeBSD). So I
> > changed it to:
> >
> > effective_cache_size =3D 27462    # typically 8KB each
>
> Apparently this formula is no longer relevant on the FreeBSD systems as
> it can cache up to almost all the available RAM. With 4GB of RAM, one
> could specify most of the RAM as being available for caching, assuming
> that nothing but PostgreSQL runs on the server -- certainly 1/2 the RAM
> would be a reasonable value to tell the planner.
>
> (This was verified by using dd:
> dd if=3D/dev/zero of=3D/usr/local/pgsql/iotest bs=3D128k count=3D16384 to=
 create
> a 2G file then
> dd if=3D/usr/local/pgsql/iotest of=3D/dev/null
>
> If you run systat -vmstat 2 you will see 0% diskaccess during the read
> of the 2G file indicating that it has, in fact, been cached)

Thank you for your reply. Does this apply to FreeBSD 5.4 or 6.0 on
amd64 (or both)?

regards
Claus