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Re: new correlation metric

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com>
Cc: Jeff Davis <pgsql(at)j-davis(dot)com>, pgsql-hackers(at)postgresql(dot)org, npboley(at)gmail(dot)com
Subject: Re: new correlation metric
Date: 2008-10-27 12:18:07
Message-ID: 14201.1225109887@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Ron Mayer <rm_pg(at)cheapcomplexdevices(dot)com> writes:
> ... I was somewhat surprised that the bitmap cost estimates didn't
> also change much.  Wouldn't the estimated # of data blocks
> read for the bitmap be roughly the same as for the index?

By definition, a bitmap scan's cost isn't affected by index order
correlation.

			regards, tom lane

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