Re: Queries with timestamp II

From: Shridhar Daithankar <shridhar(at)frodo(dot)hserus(dot)net>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Queries with timestamp II
Date: 2004-01-26 14:38:13
Message-ID: 40152655.6080605@frodo.hserus.net
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Arnau wrote:

> explain analyze select * from statistics2 where timestamp_in <
> to_timestamp( '20031201', 'YYYYMMDD' );
> NOTICE: QUERY PLAN:
>
> Seq Scan on statistics2 (cost=0.00..638.00 rows=9289 width=35) (actual
> time=0.41..688.34 rows=27867 loops=1)
> Total runtime: 730.82 msec
>
> That query is not using the index. Anybody knows what I'm doing wrong?

Since it expects large number of rows will be returned, it is favouring
sequential scan.

Given how the estimates have differed, i.e. estimated 9289 v/s actual 27867, I
sugest you up the statistics for the table using alter table. Check
http://www.postgresql.org/docs/current/static/sql-altertable.html

HTH

Shridhar

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