Re: Bitmap scan cost model (was Re: bitmap scans, btree

From: "Jeffrey W(dot) Baker" <jwbaker(at)acm(dot)org>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Bitmap scan cost model (was Re: bitmap scans, btree
Date: 2005-05-18 17:19:01
Message-ID: 1116436741.17217.27.camel@noodles
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On Wed, 2005-05-18 at 11:27 -0400, Tom Lane wrote:
> "Jeffrey W. Baker" <jwbaker(at)acm(dot)org> writes:
> > Obviously in this case sequential scan was (would have been) a huge win.
> > Incrementing random_page_cost from 4 (the default) to 5 causes the
> > planner to make a better decision.
>
> But to get the estimated cost ratio to match up with the actual cost
> ratio, we'd have to raise random_page_cost to nearly 70, which is a bit
> hard to credit. What was the platform being tested here?

i686 Linux 2.6.8 with a single 7200RPM SATA disk.

-jwb

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