From: Jim C. Nasby <jnasby@pervasive.com>
To: Vivek Khera <vivek@khera.org>
Cc: Matthew Sullivan <matthew@sorbs.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: performance problems.
Date: Wed, 30 Aug 2006 11:26:57 -0500
Message-ID: <20060830162657.GD81373@pervasive.com> (raw)
In-Reply-To: <BA0105C5-8551-49A6-B131-00D814DDFDA0@khera.org>
References: <44F55A7F.40305@sorbs.net>
<BA0105C5-8551-49A6-B131-00D814DDFDA0@khera.org>
On Wed, Aug 30, 2006 at 10:10:28AM -0400, Vivek Khera wrote:
> effective_cache_size = 27462 # `sysctl -n
> vfs.hibufspace` / 8192 (BLKSZ)
> random_page_cost = 2
You misunderstand how effective_cache_size is used. It's the *only*
memory factor that plays a role in cost estimator functions. This means
it should include the memory set aside for caching in shared_buffers.
Also, hibufspace is only talking about filesystem buffers in FreeBSD,
which AFAIK has nothing to do with total memory available for caching,
since VM pages are also used to cache data.
Basically, your best bet for setting effective_cache_size is to use the
total memory in the machine, and substract some overhead for the OS and
other processes. I'll typically subtract 1G.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, vivek@khera.org, matthew@sorbs.net
Subject: Re: performance problems.
In-Reply-To: <20060830162657.GD81373@pervasive.com>
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