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From: Robert Haas <robertmhaas@gmail.com>
To: Claudio Freire <klaussfreire@gmail.com>
Cc: Tomas Vondra <tv@fuzzy.cz>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Performance
Date: Tue, 26 Apr 2011 01:30:58 -0400
Message-ID: <D2F0DB51-7D42-4573-99CA-B72E28440B16@gmail.com> (raw)
In-Reply-To: <BANLkTikYtnzTfS8Yjc-3ap9kysXLLpJwmg@mail.gmail.com>
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	<BANLkTikYtnzTfS8Yjc-3ap9kysXLLpJwmg@mail.gmail.com>

On Apr 14, 2011, at 2:49 AM, Claudio Freire <klaussfreire@gmail.com> wrote:
> This particular factor is not about an abstract and opaque "Workload"
> the server can't know about. It's about cache hit rate, and the server
> can indeed measure that.

The server can and does measure hit rates for the PG buffer pool, but to my knowledge there is no clear-cut way for PG to know whether read() is satisfied from the OS cache or a drive cache or the platter.

...Robert



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