Horton

Re: [HACKERS] Slow count(*) again...

David Wilson <david.t.wilson@gmail.com>

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From: David Wilson <david.t.wilson@gmail.com>
To: Robert Haas <robertmhaas@gmail.com>
Cc: david@lang.hm, Vitalii Tymchyshyn <tivv00@gmail.com>, Jon Nelson <jnelson+pgsql@jamponi.net>, Mladen Gogala <mladen.gogala@vmsinfo.com>, Andrew Dunstan <andrew@dunslane.net>, Bruce Momjian <bruce@momjian.us>, Tom Lane <tgl@sss.pgh.pa.us>, Craig Ringer <craig@postnewspapers.com.au>, "pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: 2011-02-04T05:06:18Z
Lists: pgsql-hackers, pgsql-performance 
On Thu, Feb 3, 2011 at 6:05 PM, Robert Haas <robertmhaas@gmail.com> wrote:

>
> If you want to randomly pick 10,000 rows out of all the rows that are
> going to be inserted in the table without knowing in advance how many
> there will be, how do you do that?
>

Reservoir sampling, as the most well-known option:
http://en.wikipedia.org/wiki/Reservoir_sampling

-- 
- David T. Wilson
david.t.wilson@gmail.com