Re: ANALYZE sampling is too good

Поиск
Список
Период
Сортировка
От Kevin Grittner
Тема Re: ANALYZE sampling is too good
Дата
Msg-id 1386790304.24146.YahooMailNeo@web162906.mail.bf1.yahoo.com
обсуждение исходный текст
Ответ на Re: ANALYZE sampling is too good  (Gavin Flower <GavinFlower@archidevsys.co.nz>)
Ответы Re: ANALYZE sampling is too good
Список pgsql-hackers
Gavin Flower <GavinFlower@archidevsys.co.nz> wrote:

> For example, assume 1000 rows of 200 bytes and 1000 rows of 20 bytes,
> using 400 byte pages.  In the pathologically worst case, assuming
> maximum packing density and no page has both types: the large rows would
> occupy  500 pages and the smaller rows 50 pages. So if one selected 11
> pages at random, you get about 10 pages of large rows and about one for
> small rows!

With 10 * 2 = 20 large rows, and 1 * 20 = 20 small rows.

--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company



В списке pgsql-hackers по дате отправления:

Предыдущее
От: Tom Lane
Дата:
Сообщение: Re: -d option for pg_isready is broken
Следующее
От: Daniel Wood
Дата:
Сообщение: 9.3 reference constraint regression