Re: Improving N-Distinct estimation by ANALYZE

On Thu, Jan 05, 2006 at 10:12:29AM -0500, Greg Stark wrote:
> Worse, my recollection from the paper I mentioned earlier was that sampling
> small percentages like 3-5% didn't get you an acceptable accuracy. Before you
> got anything reliable you found you were sampling very large percentages of
> the table. And note that if you have to sample anything over 10-20% you may as
> well just read the whole table. Random access reads are that much slower.

If I'm reading backend/commands/analyze.c right, the heap is accessed
linearly, only reading blocks that get selected but reading them in heap
order, which shouldn't be anywhere near as bad as random access.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
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