From: Craig Ringer <ringerc@ringerc.id.au>
To: Antonio Rodriges <antonio.rrz@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: [PERFORMANCE] Insights: fseek OR read_cluster?
Date: Mon, 26 Sep 2011 15:59:39 +0800
Message-ID: <4E8030EB.60105@ringerc.id.au> (raw)
In-Reply-To: <CAPrLoNdTbOpYEvk8CTbKK6T0VjskGPNve2BCYZCg5RqwQJzvrw@mail.gmail.com>
References: <CAPrLoNeyDqHwsm80iVTDeUg8-pa+pG6D43K8O1_rG2o9KHBGLw@mail.gmail.com>
<CAPrLoNdTbOpYEvk8CTbKK6T0VjskGPNve2BCYZCg5RqwQJzvrw@mail.gmail.com>
On 24/09/2011 2:49 PM, Antonio Rodriges wrote:
> Hello,
>
> It is interesting how PostgreSQL reads the tablefiie.
> Whether its indexes store/use filesystem clusters locations containing
> required data (so it can issue a low level cluster read) or it just
> fseeks inside a file?
What is read_cluster() ? Are you talking about some kind of async
and/or direct I/O? If so, PostgreSQL is not designed for direct I/O, it
benefits from using the OS's buffer cache, I/O scheduler, etc.
IIRC Pg uses pread() to read from its data files, but I didn't go double
check in the sources to make sure.
--
Craig Ringer
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To: pgsql-performance@postgresql.org
Cc: ringerc@ringerc.id.au, antonio.rrz@gmail.com
Subject: Re: [PERFORMANCE] Insights: fseek OR read_cluster?
In-Reply-To: <4E8030EB.60105@ringerc.id.au>
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