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From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Kevin Grittner" <kgrittn@mail.com>
cc: "AI Rumman" <rummandba@gmail.com>,
	"Claudio Freire" <klaussfreire@gmail.com>,
	"Evgeny Shishkin" <itparanoia@gmail.com>,
	"Andrew Dunstan" <andrew@dunslane.net>,
	"postgres performance list" <pgsql-performance@postgresql.org>
Subject: Re: Why does the number of rows are different in actual and
 estimated.
In-reply-to: <20121214191427.80090@gmx.com>
References: <20121214191427.80090@gmx.com>
Comments: In-reply-to "Kevin Grittner" <kgrittn@mail.com>
	message dated "Fri, 14 Dec 2012 14:14:27 -0500"
Date: Fri, 14 Dec 2012 14:22:05 -0500
Message-ID: <4673.1355512925@sss.pgh.pa.us>
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"Kevin Grittner" <kgrittn@mail.com> writes:
> AI Rumman wrote:
>> Does FK Constraint help to improve performance? Or it is only
>> for maintaining data integrity?

> I'm not aware of any situation where adding a foreign key
> constraint would improve performance.

There's been talk of teaching the planner to use the existence of FK
constraints to improve plans, but I don't believe any such thing is
in the code today.

			regards, tom lane


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