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Subject: Re: Indexscan is only used if we use "limit n"
From: joao <joao.junior@bra03034.conab.gov.br>
To: sebaioni-postgresql@yahoo.com.ar
Cc: Performance PostgreSQL <pgsql-performance@postgresql.org>
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Date: Wed, 15 Aug 2007 17:02:43 -0300
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which column does your indice cover?

Em Qua, 2007-08-15 ŕs 16:36 -0300, Sebastián Baioni escreveu:
> 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.ar
> http://www.extremista.com.ar
> http://www.coolartists.com.ar
> 
> 
> ______________________________________________________________________
> 
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