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Message-ID: <81961ff50701300703r538cfd58o511ef68ee90a90e5@mail.gmail.com>
Date: Tue, 30 Jan 2007 10:03:03 -0500
From: "Chad Wagner" <chad.wagner@gmail.com>
To: "Luke Lonergan" <llonergan@greenplum.com>
Subject: Re: Querying distinct values from a large table
Cc: "Simon Riggs" <simon@2ndquadrant.com>,
 "Igor Lobanov" <ilobanov@swsoft.com>,
	"Richard Huxton" <dev@archonet.com>, pgsql-performance@postgresql.org
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On 1/30/07, Luke Lonergan <llonergan@greenplum.com> wrote:
>
> Not that it helps Igor, but we've implemented single pass sort/unique,
> grouping and limit optimizations and it speeds things up to a single
> seqscan
> over the data, from 2-5 times faster than a typical external sort.


Was that integrated back into PostgreSQL, or is that part of Greenplum's
offering?

I can't think of a way that indexing would help this situation given the
> required visibility check of each tuple.
>

I agree, using indexes as a "skinny" table is a whole other feature that
would be nice.


-- 
Chad
http://www.postgresqlforums.com/

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<div><span class="gmail_quote">On 1/30/07, <b class="gmail_sendername">Luke Lonergan</b> &lt;<a href="mailto:llonergan@greenplum.com">llonergan@greenplum.com</a>&gt; wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Not that it helps Igor, but we&#39;ve implemented single pass sort/unique,<br>grouping and limit optimizations and it speeds things up to a single seqscan<br>over the data, from 2-5 times faster than a typical external sort.
</blockquote><div><br>Was that integrated back into PostgreSQL, or is that part of Greenplum&#39;s offering? <br><br></div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I can&#39;t think of a way that indexing would help this situation given the<br>required visibility check of each tuple.<br></blockquote></div><br>I agree, using indexes as a &quot;skinny&quot; table is a whole other feature that would be nice.
<br><br clear="all"><br>-- <br>Chad<br><a href="http://www.postgresqlforums.com/">http://www.postgresqlforums.com/</a>

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