From: Michael Glaesemann <grzm@seespotcode.net>
To: Christo Du Preez <christo@mecola.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: test / live environment, major performance difference
Date: Tue, 12 Jun 2007 08:47:05 -0500
Message-ID: <6336D034-24D7-47B3-8690-9E7561E5432C@seespotcode.net> (raw)
In-Reply-To: <466EA078.20601@mecola.com>
References: <466EA078.20601@mecola.com>
On Jun 12, 2007, at 8:32 , Christo Du Preez wrote:
> I have noticed that my server never uses indexing. No matter what I
> do.
>
> As an example I took a table with about 650 rows, having a parentid
> field with an index on parentid.
>
> EXPLAIN ANALYZE
> SELECT *
> FROM layertype
> where parentid = 300;
The planner weighs the cost of the different access methods and
choses the one that it believes is lowest in cost. An index scan is
not always faster than a sequential scan. With so few rows, it's
probably faster for the server to read the whole table rather than
reading the index and looking up the corresponding row. If you want
to test this, you can set enable_seqscan to false and try running
your query again.
http://www.postgresql.org/docs/8.2/interactive/runtime-config-
query.html#RUNTIME-CONFIG-QUERY-ENABLE
Michael Glaesemann
grzm seespotcode net
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To: pgsql-performance@postgresql.org
Cc: grzm@seespotcode.net, christo@mecola.com
Subject: Re: test / live environment, major performance difference
In-Reply-To: <6336D034-24D7-47B3-8690-9E7561E5432C@seespotcode.net>
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