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Re: More On 7.2 Distributions - Estimates For Number Distinct < 0

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Mark kirkwood <markir(at)slingshot(dot)co(dot)nz>
Cc: pgsql-general(at)postgresql(dot)org
Subject: Re: More On 7.2 Distributions - Estimates For Number Distinct < 0
Date: 2001-10-29 17:15:29
Message-ID: 10382.1004375729@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-general
Mark kirkwood <markir(at)slingshot(dot)co(dot)nz> writes:
> everything looks good except for n_distinct ( its negative - should be 5) 

This is okay; see the documentation about what n_distinct means.

I'd be interested in a better rule-of-thumb for estimating whether the
number of distinct values in a column should be assumed to scale with
the total table size or not.  That 10% threshold was just pulled out
of the air...

			regards, tom lane

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