From: Jim C. Nasby <jim@nasby.net>
To: Erik Jones <erik@myemma.com>
Cc: Mark Lewis <mark.lewis@mir3.com>
Cc: Xiaoning Ding <dingxn@cse.ohio-state.edu>
Cc: pgsql-performance@postgresql.org
Subject: Re: a question about Direct I/O and double buffering
Date: Wed, 18 Apr 2007 13:07:59 -0500
Message-ID: <20070418180758.GW72669@nasby.net> (raw)
In-Reply-To: <CE3B7895-88D9-4CEC-A9EC-506AD4533300@myemma.com>
References: <46152D5D.5030602@cse.ohio-state.edu>
<4C4C834E-9304-4E23-AD15-1756921500B5@myemma.com>
<1175797629.5581.39.camel@archimedes>
<7B476592-606F-46F0-A643-9C4E5D85CE6E@myemma.com>
<1175802972.5581.56.camel@archimedes>
<CE3B7895-88D9-4CEC-A9EC-506AD4533300@myemma.com>
On Thu, Apr 05, 2007 at 03:10:43PM -0500, Erik Jones wrote:
> Nope. What we never tracked down was the factor of 10 drop in
> database transactions, not disk transactions. The write volume was
> most definitely due to the direct io setting -- writes are now being
> done in terms of the system's block size where as before they were
> being done in terms of the the filesystem's cache page size (as it's
> in virtual memory). Basically, we do so many write transactions that
> the fs cache was constantly paging.
Did you try decreasing the size of the cache pages? I didn't realize
that Solaris used a different size for cache pages and filesystem
blocks. Perhaps the OS was also being too aggressive with read-aheads?
My concern is that you're essentially leaving a lot of your memory
unused this way, since shared_buffers is only set to 1.6G.
BTW, did you ever increase the parameter that controls how much memory
Solaris will use for filesystem caching?
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
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To: pgsql-performance@postgresql.org
Cc: jim@nasby.net, erik@myemma.com, mark.lewis@mir3.com, dingxn@cse.ohio-state.edu
Subject: Re: a question about Direct I/O and double buffering
In-Reply-To: <20070418180758.GW72669@nasby.net>
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