Re: Bitmap scan cost model (was Re: bitmap scans, btree scans, and tid order)

From: Manfred Koizar <mkoi-pg(at)aon(dot)at>
To: "Jeffrey W(dot) Baker" <jwbaker(at)acm(dot)org>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Bitmap scan cost model (was Re: bitmap scans, btree scans, and tid order)
Date: 2005-05-18 12:35:51
Message-ID: a2dm815pnm26564oeq2bniuhp909pkpfis@email.aon.at
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On Tue, 17 May 2005 22:12:17 -0700, "Jeffrey W. Baker" <jwbaker(at)acm(dot)org>
wrote:
>Incrementing random_page_cost from 4 (the default) to 5 causes the
>planner to make a better decision.

We have such a low default random_page_cost primarily to mask other
problems in the optimizer, two of which are

. multi-column index correlation

. interpolation between min_IO_Cost and max_IO_cost which approximates
max_IO_cost too fast.

Servus
Manfred

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