Re: Searching for the cause of a bad plan

Поиск
Список
Период
Сортировка
От Simon Riggs
Тема Re: Searching for the cause of a bad plan
Дата
Msg-id 1190396352.4202.109.camel@ebony.site
обсуждение исходный текст
Ответ на Re: Searching for the cause of a bad plan  (Tom Lane <tgl@sss.pgh.pa.us>)
Ответы Re: Searching for the cause of a bad plan  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-performance
On Fri, 2007-09-21 at 12:08 -0400, Tom Lane wrote:
> Csaba Nagy <nagy@ecircle-ag.com> writes:
> > Looking at Plan 2, it looks like the "limit" step is estimating wrongly
> > it's cost.
>
> The reason you get a bad plan is that this rowcount estimate is so far
> off:

That's true, but its not relevant, since the query would still be fast
even if that estimate was exactly right. With LIMIT 10, it wouldn't
matter how many rows were there as long as there were more than 10. The
true execution cost is limited, the cost model is not.

--
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com


В списке pgsql-performance по дате отправления:

Предыдущее
От: brauagustin-susc@yahoo.com.ar
Дата:
Сообщение: Re: Low CPU Usage
Следующее
От: Simon Riggs
Дата:
Сообщение: Re: Query planner unaware of possibly best plan