Date: Mon, 23 May 2005 16:29:49 -0700 From: John-Mark Gurney <gurney_j@resnet.uoregon.edu> To: Vivek Khera <vivek@khera.org> Cc: freebsd-stable@freebsd.org, freebsd-amd64@freebsd.org Subject: Re: Manipulating disk cache (buf) settings Message-ID: <20050523232948.GJ959@funkthat.com> In-Reply-To: <1F46458B-2524-42AB-8B3D-0F54F485241B@khera.org> References: <1116860293.10083.43.camel@lanshark.dmv.com> <20050523174415.GI959@funkthat.com> <1F46458B-2524-42AB-8B3D-0F54F485241B@khera.org>
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Vivek Khera wrote this message on Mon, May 23, 2005 at 17:17 -0400:
> On May 23, 2005, at 1:44 PM, John-Mark Gurney wrote:
>
> >This is incorrect... FreeBSD merged the vm and buf systems a while
> >back,
> >so all of memory is used as a disk cache.. The buf cache is still
> >used
> >for filesystem meta data (and for pending writes of files, but
> >those buf's
> >reference the original page, not local storage)...
> >
>
> Cool... So what would you recommend telling an application like
> Postgres what the cache size is? All of RAM? That seems unlikely
> given much of the ram is used for other things. Is there no upper
> bound in how much RAM will be used for the cache?
I'm not familar host Postgres uses the cache number to change it's
behavior, but I would say choose a responable amount of memory that
you expect to regularly have available on the system... If you are
only using it for db, and a few other small processes, 512meg less
than ram is probably reasonable...
The other way is to try a few different values and see how it impacts
performance..
--
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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