Date: Thu, 16 Feb 2006 15:39:23 -0500
From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-sql@postgresql.org
Subject: Re: Using EXPLAIN-ANALYZE
Message-ID: <20060216203923.GA9872@phlogiston.dyndns.org>
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On Thu, Feb 16, 2006 at 12:07:10PM -0800, Kashmira Patel (kupatel) wrote:
> Hi all,
>    I am pretty new to using Postrgres, and have been looking at the
> messages in this forum for a while. I have noticed that the use of
> EXPLAIN-ANALYZE is recommended quite a lot. I read the Postgres docs,
> but am not quite sure I understand how this works. Is there some
> tutorial or any other documentation how this can be used?

Well, here's the short version:

EXPLAIN [query] tells you what the planner _thinks_ it should do.

EXPLAIN ANALYZE [query] tells you what the planner thinks it should
do, and also executes the query and reports back how long every step
took, how many rows were returned, &c.  (For this reason, you want to
wrap it in BEGIN;...;ROLLBACK; if it changes data.)

For more, see the EXPLAIN EXPLAINED tutorial on
techdocs.postgresql.org
(<http://techdocs.postgresql.org/oscon2005/robert.treat/OSCON_Explaining_Explain_Public.sxi>)

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
In the future this spectacle of the middle classes shocking the avant-
garde will probably become the textbook definition of Postmodernism. 
                --Brad Holland