| From: | David Wilson <david(dot)t(dot)wilson(at)gmail(dot)com> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | david(at)lang(dot)hm, Vitalii Tymchyshyn <tivv00(at)gmail(dot)com>, Jon Nelson <jnelson+pgsql(at)jamponi(dot)net>, Mladen Gogala <mladen(dot)gogala(at)vmsinfo(dot)com>, Andrew Dunstan <andrew(at)dunslane(dot)net>, Bruce Momjian <bruce(at)momjian(dot)us>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>, "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Slow count(*) again... |
| Date: | 2011-02-04 05:06:18 |
| Message-ID: | AANLkTi=A-70EgJ8yWDCn4hbyCaA0nFJFA3+zedan=nLS@mail.gmail.com |
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| Lists: | pgsql-hackers pgsql-performance |
On Thu, Feb 3, 2011 at 6:05 PM, Robert Haas <robertmhaas(at)gmail(dot)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(dot)t(dot)wilson(at)gmail(dot)com
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