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

Sam Gendler <sgendler@ideasculptor.com>

From: Samuel Gendler <sgendler@ideasculptor.com>

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

Cc: Robert Haas <robertmhaas@gmail.com>, 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: 2011-02-04T06:36:20Z

Lists: pgsql-hackers, pgsql-performance

Neat.  That was my 'you learn something every day' moment.  Thanks.

On Thu, Feb 3, 2011 at 9:06 PM, David Wilson <david.t.wilson@gmail.com>wrote:

>
>
> 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
>