From: Martin Nickel <martin@portant.com>
To: pgsql-performance@postgresql.org
Subject: Sequential scan on FK join
Date: Wed, 12 Oct 2005 15:40:24 -0500
Message-ID: <pan.2005.10.12.20.40.22.703085@portant.com> (raw)
All,
I can see why the query below is slow. The lead table is 34 million rows,
and a sequential scan always takes 3+ minutes. Mailing_id is the PK for
mailing and is constrained as a foreign key (NULLS allowed) in lead.
There is an index on lead.mailing_id. I've just run VACUUM ANALYZE on
lead. I don't understand why it isn't being used.
Thanks for your help,
Martin Nickel
SELECT m.mailcode, l.lead_id
FROM mailing m
INNER JOIN lead l ON m.mailing_id = l.mailing_id
WHERE (m.maildate >= '2005-7-01'::date
AND m.maildate < '2005-8-01'::date)
-- takes 510,145 ms
EXPLAIN SELECT m.mailcode, l.lead_id
FROM mailing m
INNER JOIN lead l ON m.mailing_id = l.mailing_id
WHERE (m.maildate >= '2005-7-01'::date
AND m.maildate < '2005-8-01'::date)
Hash Join (cost=62.13..2001702.55 rows=2711552 width=20)
Hash Cond: ("outer".mailing_id = "inner".mailing_id)
-> Seq Scan on lead l (cost=0.00..1804198.60 rows=34065260 width=8)
-> Hash (cost=61.22..61.22 rows=362 width=20)
-> Index Scan using mailing_maildate_idx on mailing m (cost=0.00..61.22 rows=362 width=20)
Index Cond: ((maildate >= '2005-07-01'::date) AND (maildate < '2005-08-01'::date))
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To: pgsql-performance@postgresql.org
Cc: martin@portant.com
Subject: Re: Sequential scan on FK join
In-Reply-To: <pan.2005.10.12.20.40.22.703085@portant.com>
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