From: Florian Weimer <fweimer@bfk.de>
To: pgsql-performance@postgresql.org
Subject: pg_trgm performance
Date: Mon, 15 Jan 2007 11:16:36 +0100
Message-ID: <82mz4k4mt7.fsf@mid.bfk.de> (raw)
I've got a table with a few million rows, consisting of a single text
column. The average length is about 17 characters. For the sake of
an experiment, I put a trigram index on that table. Unfortunately, %
queries without smallish LIMITs are ridiculously slow (they take
longer than an hour). A full table scan with a "WHERE similarity(...)
>= 0.4" clause completes in just a couple of minutes. The queries
only select a few hundred rows, so an index scan has got a real chance
to be faster than a sequential scan.
Am I missing something? Or are trigrams just a poor match for my data
set? Are the individual strings too long, maybe?
(This is with PostgreSQL 8.2.0, BTW.)
--
Florian Weimer <fweimer@bfk.de>
BFK edv-consulting GmbH http://www.bfk.de/
Kriegsstraße 100 tel: +49-721-96201-1
D-76133 Karlsruhe fax: +49-721-96201-99
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To: pgsql-performance@postgresql.org
Cc: fweimer@bfk.de
Subject: Re: pg_trgm performance
In-Reply-To: <82mz4k4mt7.fsf@mid.bfk.de>
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