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To: Ehab Galal <ehabgalal123@hotmail.com>
cc: "pgsql-sql@postgresql.org" <pgsql-sql@postgresql.org>
Subject: Re: materialize 
In-reply-to: <BAY138-W1297C42D3E676BE815771E96750@phx.gbl> 
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Comments: In-reply-to Ehab Galal <ehabgalal123@hotmail.com>
	message dated "Mon, 26 Nov 2007 16:17:14 -0500"
Date: Mon, 26 Nov 2007 16:53:45 -0500
Message-ID: <4140.1196114025@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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Ehab Galal <ehabgalal123@hotmail.com> writes:
> I was wondering why do we need the Materialize node in the plan below when i explain a query? 

It's cheaper to scan a materialized rowset many times than a raw table
--- we don't need to re-access shared memory nor re-check row visibility.

			regards, tom lane