From: Michael Glaesemann <grzm@seespotcode.net>
To: Tyler Durden <tylersticky@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Seq Scan
Date: Fri, 1 Jun 2007 12:03:30 -0500
Message-ID: <96F60F91-F3A7-4134-8DD0-E519C8941CDB@seespotcode.net> (raw)
In-Reply-To: <ab07320e0706010948m7c4eb1b8s9cdaf79b1c400125@mail.gmail.com>
References: <ab07320e0706010948m7c4eb1b8s9cdaf79b1c400125@mail.gmail.com>
On Jun 1, 2007, at 11:48 , Tyler Durden wrote:
> I'm having some problems in performance in a simple select count(id)
> from....
Unrestricted count() (i.e., no WHERE clause) will perform a
sequential scan. If you're looking for faster ways to store table row
count information, please search the archives, as this has been
discussed many times before.
> # explain select (id) from table_name;
> -[ RECORD
> 1 ]----------------------------------------------------------------
> QUERY PLAN | Seq Scan on table_name (cost=0.00..8601.30
> rows=266730 width=4)
The query returns the id column value for each row in the table. The
fastest way to do this is visiting every row., i.e., a sequential
scan. Using an index would require (1) looking in the index and (2)
looking up the corresponding row.
Michael Glaesemann
grzm seespotcode net
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To: pgsql-performance@postgresql.org
Cc: grzm@seespotcode.net, tylersticky@gmail.com
Subject: Re: Seq Scan
In-Reply-To: <96F60F91-F3A7-4134-8DD0-E519C8941CDB@seespotcode.net>
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