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To: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
cc: "Robert Haas" <robertmhaas@gmail.com>,
	"Achilleas Mantzios" <achill@matrix.gatewaynet.com>,
	pgsql-performance@postgresql.org
Subject: Re: "NOT IN" substantially slower in 9.0.2 than 8.3.13 - NOT EXISTS
	runs fast in both 8.3.13 and 9.0.2
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Comments: In-reply-to "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
	message dated "Fri, 21 Jan 2011 14:00:44 -0600"
Date: Fri, 21 Jan 2011 15:22:24 -0500
Message-ID: <19623.1295641344@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>
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"Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes:
> Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> If it should be less than 1, then what?
 
> 1 - (estimated tuples / estimated distinct values) ?

Uh, no.  The number we're after is the probability that an outer tuple
has at least one unequal value in the inner relation.  This is not 1
minus the probability that a *specific* inner value is equal, which is
what I think your formula is estimating.

			regards, tom lane