Date: Fri, 06 Jul 2007 12:03:12 -0400
From: "Jignesh K. Shah" <J.K.Shah@Sun.COM>
Subject: Re: Direct I/O
In-reply-to: <BAY126-W47B86724087E7C49F49E74A9010@phx.gbl>
To: lai yoke hman <lllhman@hotmail.com>
Cc: pgsql-performance@postgresql.org
Message-id: <468E67C0.60405@sun.com>
Organization: Sun Microsystems
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On Solaris you just look at the mount options on the file system and see
if there is a forcedirectio option enabled. Generally since PostgreSQL
doesn't use any special options for enabling directio that's a known way
to figure it out on Solaris. Atleast on Solaris the performance over
buffered filesystem is better for many workloads but not always. Plus
you typically see a small reduction in CPU usage (system) and ofcourse
memory.

However depending on workload, you may see increased latency in writes
but generally that's not the problem in many workloads since its the
multiple writes to the same file which is better using concurrentio
(modified directio) in Solaris.

As for Linux I will leave that to other experts ..

-Jignesh


lai yoke hman wrote:
> Hello,
> How can I know my PostgreSQL 8 is using direct I/O or buffered I/O? If using buffered I/O, how can I enable direct I/O? What is the performance difference of them?
> This is urgent, Thanks.
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