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Date: Fri, 21 Sep 2007 11:35:15 -0500
From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
To: "Kamen Stanev" <hambai@gmail.com>,
	<pgsql-performance@postgresql.org>
Subject: Re: query io stats and finding a slow query
References: <de5063670709201436y5cbff0d0k70ade289a4c68199@mail.gmail.com>
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>>> On Thu, Sep 20, 2007 at  4:36 PM, in message
<de5063670709201436y5cbff0d0k70ade289a4c68199@mail.gmail.com>, "Kamen =
Stanev"
<hambai@gmail.com> wrote:=20
>=20
> Is there a way to find which query is doing large io operations and/or =
which
> is using cached data and which is reading from disk.
=20
A big part of your cache is normally in the OS, which makes that tough.
=20
> please share your experience on how do you decide which
> queries to optimize and how to reorganize your database?
=20
We base this on two things -- query metrics from our application framework
and user complaints about performance.

> Is there any tools that you use to profile your database.
 =20
Many people set log_min_duration_statement to get a look at long-running
queries.
=20
When you identify a problem query, running it with EXPLAIN ANALYZE in =
front
will show you the plan with estimated versus actual counts, costs, and =
time.
This does actually execute the query (unlike EXPLAIN without ANALYZE).
=20
-Kevin
=20