On Sun, Oct 24, 2004 at 04:11:53PM -0400, Tom Lane wrote:
> But the LIMIT will cut the cost of the seqscan case too. Given the
> numbers you posit above, about one row in five will have 'myval', so a
> seqscan can reasonably expect to hit the first matching row in the first
> page of the table. This is still cheaper than doing an index scan
> (which must require reading at least one index page plus at least one
> table page).
>
> The test case you are showing is probably suffering from nonrandom
> placement of this particular data value; which is something that the
> statistics we keep are too crude to detect.
Isn't that exactly what pg_stats.correlation is?
--
Jim C. Nasby, Database Consultant decibel@decibel.org
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