Message-ID: <446B7241.2060409@modgraph-usa.com>
Date: Wed, 17 May 2006 11:58:09 -0700
From: "Craig A. James" <cjames@modgraph-usa.com>
User-Agent: Mozilla Thunderbird 1.0.6 (X11/20050716)
MIME-Version: 1.0
To: Tom Lane <tgl@sss.pgh.pa.us>
CC: Bruno Wolff III <bruno@wolff.to>, pgsql-performance@postgresql.org
Subject: Re: Optimizer: limit not taken into account
References: <44699C6C.80302@tweakers.net> <4469D173.50406@sun.com>
	<4469D986.6090300@tweakers.net> <4469F55A.7040004@sun.com>
	<446A1520.2020601@tweakers.net> <446B0409.7050902@sun.com>
	<446B0ED2.5030909@tweakers.net> <446B474C.2050803@modgraph-usa.com>
	<20060517174426.GA14567@wolff.to> <24245.1147890622@sss.pgh.pa.us>
In-Reply-To: <24245.1147890622@sss.pgh.pa.us>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit

Tom Lane wrote:
> There is not anything in there that considers whether the table's
> physical order is so nonrandom that the search will take much longer
> than it would given uniform distribution.  It might be possible to do
> something with the correlation statistic in simple cases ...

In this case, the rows are not random at all, in fact they're inserted from a sequence, then rows are deleted as they are processed.  If the planner is hoping for random physical distribution, this particular case is exactly wrong. 

Craig