From: | Josh Berkus <josh(at)agliodbs(dot)com> |
---|---|
To: | Karl Denninger <karl(at)Denninger(dot)Net>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Why is query selecting sequential? |
Date: | 2004-02-06 21:51:39 |
Message-ID: | 200402061351.39084.josh@agliodbs.com |
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Lists: | pgsql-performance |
Karl,
> SubPlan
> -> Seq Scan on forumlog (cost=0.00..1.18 rows=1 width=8)
> Filter: ((login = '%s'::text) AND (forum = '%s'::text) AND
(number = $0))
> Why is the subplan using a sequential scan? At minimum the index on the
> post number ("forumlog_number") should be used, no? What would be even
> better would be a set of indices that allow at least two (or even all three)
> of the keys in the inside SELECT to be used.
It's using a seq scan because you have only 1 row in the table. Don't
bother testing performance before your database is populated.
PostgreSQL doesn't just use an index because it's there; it uses and index
because it's faster than not using one.
If there is more than one row in the table, then:
1) run ANALYZE forumlog;
2) Send us the EXPLAIN ANALYZE, not just the explain for the query.
--
-Josh Berkus
Aglio Database Solutions
San Francisco
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