From: Sebastián Baioni <sebaioni-postgresql@yahoo.com.ar>
To: Performance PostgreSQL <pgsql-performance@postgresql.org>
Subject: Indexscan is only used if we use "limit n"
Date: Wed, 15 Aug 2007 16:36:45 -0300 (ART)
Message-ID: <377451.48008.qm@web36104.mail.mud.yahoo.com> (raw)
Hello,
Whe are running PostgreSQL 8.2.0 on amd64-portbld-freebsd6.2, compiled by GCC cc (GCC) 3.4.6 [FreeBSD] 20060305.
The query only uses the index if we have a "limit n":
Without "Limit n"
explain
select esapcuit, esapcuil
from esact00 t1
order by esapcuit, esapcuil
Sort (cost=843833.82..853396.76 rows=3825177 width=30)
Sort Key: esapcuit, esapcuil
-> Seq Scan on esact00 t1 (cost=0.00..111813.77 rows=3825177 width=30)
With "Limit n"
explain
select esapcuit, esapcuil
from esact00 t1
order by esapcuit, esapcuil
limit 1
Limit (cost=0.00..1.86 rows=1 width=30)
-> Index Scan using uesact002 on esact00 t1 (cost=0.00..7129736.89 rows=3825177 width=30)
Our postgresql.conf is:
enable_bitmapscan = on
enable_hashagg = on
enable_hashjoin = on
enable_indexscan = on
enable_mergejoin = on
enable_nestloop = on
enable_seqscan = on
enable_sort = on
enable_tidscan = on
Thank you.
Sebastián
Sebastián Baioni
http://www.acomplejados.com.arhttp://www.extremista.com.arhttp://www.coolartists.com.ar
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Subject: Re: Indexscan is only used if we use "limit n"
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