From: Claus Guttesen <kometen@gmail.com>
To: Sven Willenberger <sven@dmv.com>
Cc: Jon Brisbin <jon.brisbin@npcinternational.com>
Cc: pgsql-performance@postgresql.org
Subject: effective cache size on FreeBSD (WAS: Performance on SUSE w/ reiserfs)
Date: Tue, 11 Oct 2005 16:54:31 +0200
Message-ID: <b41c75520510110754g534d9fa8u@mail.gmail.com> (raw)
> > I have a postgresql 7.4.8-server with 4 GB ram.
> > #effective_cache_size = 1000 # typically 8KB each
> >
> > This is computed by sysctl -n vfs.hibufspace / 8192 (on FreeBSD). So I
> > changed it to:
> >
> > effective_cache_size = 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=/dev/zero of=/usr/local/pgsql/iotest bs=128k count=16384 to create
> a 2G file then
> dd if=/usr/local/pgsql/iotest of=/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
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To: pgsql-performance@postgresql.org
Cc: kometen@gmail.com, sven@dmv.com, jon.brisbin@npcinternational.com
Subject: Re: effective cache size on FreeBSD (WAS: Performance on SUSE w/ reiserfs)
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