From: Richard Huxton <dev@archonet.com>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Igor Lobanov <ilobanov@swsoft.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Querying distinct values from a large table
Date: Tue, 30 Jan 2007 14:11:48 +0000
Message-ID: <45BF5224.3070805@archonet.com> (raw)
In-Reply-To: <1170165856.3681.54.camel@silverbirch.site>
References: <45BF02DE.7080605@swsoft.com>
<45BF0C13.3070003@archonet.com>
<45BF10D7.3040203@swsoft.com>
<1170165856.3681.54.camel@silverbirch.site>
Simon Riggs wrote:
> 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.
Well, even if the sort was instant it's only going to get him down to
20secs.
--
Richard Huxton
Archonet Ltd
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: dev@archonet.com, simon@2ndquadrant.com, ilobanov@swsoft.com
Subject: Re: Querying distinct values from a large table
In-Reply-To: <45BF5224.3070805@archonet.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox