Date: Wed, 23 Feb 2005 09:25:26 -0500
From: Andrew Sullivan <ajs@crankycanuck.ca>
To: pgsql-sql@postgresql.org
Subject: Re: PostgreSQL ignores my indexes
Message-ID: <20050223142526.GA9072@phlogiston.dyndns.org>
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This is probably better on -performance, and is certainly a FAQ. 
But. . .

On Wed, Feb 23, 2005 at 03:01:52PM +0100, Thomas Braad Toft wrote:
> 
> Table device contains 5285 rows, tmeevent contains 834912 rows.
                        ^^^^                         ^^^^^^

> ->  Seq Scan on tmeevent  (cost=0.00..23606.12 rows=834912 width=138)
> (actual time=0.04..2193.97 rows=834912 loops=1)
                                  ^^^^^^

> ->  Seq Scan on device  (cost=0.00..564.85 rows=5285 width=29) (actual
> time=0.04..25.07 rows=5285 loops=1)
                        ^^^^

> Why isn't the planner using my indexes? I tried making them as both rtree

Because there's no advantage to using an index when you are fetching
100% of both tables.  This is the most efficient plan.  Of course,
it's an open question whether you want to get 100% of both tables. 
But that's what you're doing, and using the index would be more
expoensive than this.

A

-- 
Andrew Sullivan  | ajs@crankycanuck.ca
Information security isn't a technological problem.  It's an economics
problem.
		--Bruce Schneier