Message-ID: <4FFB6E45.50708@ringerc.id.au>
Date: Tue, 10 Jul 2012 07:50:29 +0800
From: Craig Ringer <ringerc@ringerc.id.au>
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To: Misa Simic <misa.simic@gmail.com>
CC: Andrew Dunstan <andrew@dunslane.net>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Subject: Re: Paged Query
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On 07/10/2012 06:24 AM, Misa Simic wrote:
> Hi Andrew,
>
> Sure... We are sending data in Json to clients
>
> {
> total:6784,
> data:[50 rows for desired page]
> }
>
> SELECT count(*) FROM table - without where, without joins used to have
> bad performance... However, in real scenario we have never had the case
> without joins and where... Join columns are always indexed, and we
> always try to put indexes on columns what will mostly be used in where
> in usual queries...

When/if you do need a count of a single table without any filters, a 
common trick is to use table statistics to return an approximation. If 
your autovaccum is running regularly it's usually a very good 
approximation, too.

Sounds like this hack may become unnecessary in 9.2 though.

--
Craig Ringer