From: Simon Riggs <simon@2ndquadrant.com>
To: Igor Lobanov <ilobanov@swsoft.com>
Cc: Richard Huxton <dev@archonet.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Querying distinct values from a large table
Date: Tue, 30 Jan 2007 14:04:15 +0000
Message-ID: <1170165856.3681.54.camel@silverbirch.site> (raw)
In-Reply-To: <45BF10D7.3040203@swsoft.com>
References: <45BF02DE.7080605@swsoft.com>
<45BF0C13.3070003@archonet.com>
<45BF10D7.3040203@swsoft.com>
On Tue, 2007-01-30 at 15:33 +0600, Igor Lobanov wrote:
> explain analyze select distinct a, b from tbl
>
> EXPLAIN ANALYZE output is:
>
> Unique (cost=500327.32..525646.88 rows=1848 width=6) (actual
> time=52719.868..56126.356 rows=5390 loops=1)
> -> Sort (cost=500327.32..508767.17 rows=3375941 width=6) (actual
> time=52719.865..54919.989 rows=3378864 loops=1)
> Sort Key: a, b
> -> Seq Scan on tbl (cost=0.00..101216.41 rows=3375941
> width=6) (actual time=16.643..20652.610 rows=3378864 loops=1)
> Total runtime: 57307.394 ms
All your time is in the sort, not in the SeqScan.
Increase your work_mem.
--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com
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To: pgsql-performance@postgresql.org
Cc: simon@2ndquadrant.com, ilobanov@swsoft.com, dev@archonet.com
Subject: Re: Querying distinct values from a large table
In-Reply-To: <1170165856.3681.54.camel@silverbirch.site>
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