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Re: estimating # of distinct values

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tomas Vondra" <tv(at)fuzzy(dot)cz>,"Robert Haas" <robertmhaas(at)gmail(dot)com>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: estimating # of distinct values
Date: 2010-12-27 22:49:51
Message-ID: 4D18C3AF0200002500038BEF@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-hackers
Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
 
> With respect to (b), I think I'd need to see a much more detailed
> design for how you intend to make this work.  Off the top of my
> head there seems to be some pretty serious feasibility problems.
 
I had one random thought on that -- it seemed like a large concern
was that there would need to be at least an occasional scan of the
entire table to rebuild the distinct value information.  Don't we
already require an occasional scan of the entire table for freezing
transaction IDs?  Could this be part of any vacuum of the entire
table?
 
-Kevin

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