Horton

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

Manfred Koizar <mkoi-pg@aon.at>

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From: Manfred Koizar <mkoi-pg@aon.at>
To: "Jeffrey W. Baker" <jwbaker@acm.org>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgresql.org
Date: 2005-05-18T12:35:51Z
Lists: pgsql-hackers 
On Tue, 17 May 2005 22:12:17 -0700, "Jeffrey W. Baker" <jwbaker@acm.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