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To: "Daniel Caune" <daniel.caune@ubisoft.com>
cc: "Andrew Sullivan" <ajs@crankycanuck.ca>, pgsql-sql@postgresql.org
Subject: Re: How to force PostgreSQL using an index 
In-reply-to: <1E293D3FF63A3740B10AD5AAD88535D20190926B@UBIMAIL1.ubisoft.org> 
References: <1E293D3FF63A3740B10AD5AAD88535D20190926B@UBIMAIL1.ubisoft.org>
Comments: In-reply-to "Daniel Caune" <daniel.caune@ubisoft.com>
	message dated "Wed, 15 Feb 2006 17:26:57 -0500"
Date: Wed, 15 Feb 2006 17:47:15 -0500
Message-ID: <20471.1140043635@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Daniel Caune" <daniel.caune@ubisoft.com> writes:
> SELECT <some-columns>
>   FROM GSLOG_EVENT
>   WHERE EVENT_NAME = 'player-status-update'
>     AND EVENT_DATE_CREATED >= <start-time>
>     AND EVENT_DATE_CREATED < <end-time>

> I have an index on EVENT_DATE_CREATED that does it job.  But I though
> that I can help my favourite PostgreSQL if I create a composite index on
> EVENT_DATE_CREATED and EVENT_NAME (in that order as EVENT_DATE_CREATED
> is more dense that EVENT_NAME).

Wrong ... should be EVENT_NAME first.  Think about the sort order of the
data to see why --- your query represents a contiguous subset of the
index if EVENT_NAME is first, but not if EVENT_DATE_CREATED is first.

			regards, tom lane