Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT - Mailing list pgsql-hackers

From Tom Lane
Subject Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT
Date
Msg-id 7785.1238983236@sss.pgh.pa.us
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In response to Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT  (Robert Haas <robertmhaas@gmail.com>)
Responses Re: ALTER TABLE ... ALTER COLUMN ... SET DISTINCT  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-hackers
Robert Haas <robertmhaas@gmail.com> writes:
> On Sun, Apr 5, 2009 at 7:56 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> [ shrug... ] �Precision is not important for this value: we are not
>> anywhere near needing more than six significant digits for our
>> statistical estimates. �Range, on the other hand, could be important
>> when dealing with really large tables.

> I thought about that, and if you think that's better, I can implement
> it that way.  Personally, I'm unconvinced.  The use case for
> specifying a number of distinct values in excess of 2 billion as an
> absolute number rather than as a percentage of the table size seems
> pretty weak to me.

I was more concerned about the other end of it.  Your patch sets a
not-too-generous lower bound on the percentage that can be represented ...
        regards, tom lane


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