From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: kouber@saparev.com
Cc: pgsql-performance@postgresql.org
Subject: Re: LIMIT confuses the planner
Date: Mon, 23 Feb 2009 10:09:49 -0500
Message-ID: <3562.1235401789@sss.pgh.pa.us> (raw)
In-Reply-To: <603c8f070902230653v346f5b5cm6aeceedce7903f5@mail.gmail.com>
References: <49A295F0.5010405@saparev.com>
<603c8f070902230653v346f5b5cm6aeceedce7903f5@mail.gmail.com>
Robert Haas <robertmhaas@gmail.com> writes:
> If you left seq_page_cost (which isn't mentioned here) at the default
> value but reduced random_page_cost to 0.1, then you have
> random_page_cost < seq_page_cost. That's probably Bad.
... well, it's certainly going to push the planner to believe indexscans
are cheaper than sorts no matter what.
The previously noted rowcount estimation problem might be a bigger issue
in this particular case, but I agree this is a Bad Idea.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, robertmhaas@gmail.com, kouber@saparev.com
Subject: Re: LIMIT confuses the planner
In-Reply-To: <3562.1235401789@sss.pgh.pa.us>
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