Query not using the indexes properly.

From: Tim Uckun <timuckun(at)gmail(dot)com>
To: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Query not using the indexes properly.
Date: 2009-10-02 01:47:23
Message-ID: 855e4dcf0910011847q2779cbdfpdff04d8b742b6270@mail.gmail.com
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I have a pretty simple query on a pretty simple table with about 60
million records in it.

This is the query.

SELECT * FROM "changes" WHERE (id > 1935759 and company_id = 4 and
source_model_name = 'CommissionedVisit') ORDER BY id ASC LIMIT 1

The id field is the primary key. The other fields are indexed
(company_id and source_model_name).

This query takes about 30 seconds to run on a pretty beefy machine.

Here is the explain.

"Limit (cost=0.00..7.46 rows=1 width=45) (actual
time=28799.712..28799.712 rows=0 loops=1)"
" -> Index Scan using changes_pkey on changes
(cost=0.00..2331939.52 rows=312519 width=45) (actual
time=28799.710..28799.710 rows=0 loops=1)"
" Index Cond: (id > 1935759)"
" Filter: ((company_id = 4) AND ((source_model_name)::text =
'CommissionedVisit'::text))"
"Total runtime: 28799.749 ms"

It seem to me that it's ignoring the indexes on the text fields. Is
that right?

I did a vacuum analyze on the table but that didn't seem to help at all.

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