From: Gregory Stark <stark@enterprisedb.com>
To: Scott Carey <scott@richrelevance.com>
Cc: pgsql-performance\@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Query planner cost estimate less than the sum of its parts?
Date: Wed, 05 Nov 2008 21:22:09 +0000
Message-ID: <877i7hc1ha.fsf@oxford.xeocode.com> (raw)
In-Reply-To: <a1ec7d000811051200m64561fd9l5a10983d4d40f097@mail.gmail.com>
References: <a1ec7d000811051200m64561fd9l5a10983d4d40f097@mail.gmail.com>
"Scott Carey" <scott@richrelevance.com> writes:
> Certainly, a cost estimate that is ... LESS than one of the sub sections of
> the query is wrong. This was one hell of a broken query, but it at least
> should have taken an approach that was not a nested loop, and I'm curious if
> that choice was due to a bad estimate here.
>
> Nested Loop IN Join (cost=0.00..3850831.86 rows=128266 width=8)
Because it's an IN join it doesn't have to run the inner join to completion.
Once it finds a match it can return the outer tuple and continue to the next
outer tuple.
--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com
Ask me about EnterpriseDB's 24x7 Postgres support!
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To: pgsql-performance@postgresql.org
Cc: stark@enterprisedb.com, scott@richrelevance.com
Subject: Re: Query planner cost estimate less than the sum of its parts?
In-Reply-To: <877i7hc1ha.fsf@oxford.xeocode.com>
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