From: Jim C. Nasby <jnasby@pervasive.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrus <eetasoft@online.ee>
Cc: pgsql-performance@postgresql.org
Subject: Re: Why date index is not used
Date: Thu, 8 Jun 2006 16:57:45 -0500
Message-ID: <20060608215745.GE45331@pervasive.com> (raw)
In-Reply-To: <196.1149794455@sss.pgh.pa.us>
References: <e69rq9$2a1b$1@news.hub.org>
<196.1149794455@sss.pgh.pa.us>
On Thu, Jun 08, 2006 at 03:20:55PM -0400, Tom Lane wrote:
> "Andrus" <eetasoft@online.ee> writes:
> > Why Postgres 8.1 does not use makse_kuupaev_idx index in the following query
> > ?
>
> Because it doesn't help --- the system still has to do the sort.
> You'd need a two-column index on both of the ORDER BY columns to avoid
> sorting.
And even then you better have a pretty high correlation on the first
column, otherwise you'll still get a seqscan.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
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To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, tgl@sss.pgh.pa.us, eetasoft@online.ee
Subject: Re: Why date index is not used
In-Reply-To: <20060608215745.GE45331@pervasive.com>
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