Re: Why does the number of rows are different in actual and estimated.

Поиск
Список
Период
Сортировка
От AI Rumman
Тема Re: Why does the number of rows are different in actual and estimated.
Дата
Msg-id CAGoODpdQsOE7fwT47SOhSq7QcQcfEKSPHANf7Yu_GjJYRVT-hA@mail.gmail.com
обсуждение исходный текст
Ответ на Re: Why does the number of rows are different in actual and estimated.  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-performance
So I am going to change 
join_collapse_limit 
and 
from_collapse_limit 
to 20.

Do I need to set geqo_threshold to greater than 20. Now it is 12 ( default).

And could you let me know why geqo_optimizer is not working good in this case?



On Fri, Dec 14, 2012 at 2:22 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
"Kevin Grittner" <kgrittn@mail.com> writes:
> AI Rumman wrote:
>> Does FK Constraint help to improve performance? Or it is only
>> for maintaining data integrity?

> I'm not aware of any situation where adding a foreign key
> constraint would improve performance.

There's been talk of teaching the planner to use the existence of FK
constraints to improve plans, but I don't believe any such thing is
in the code today.

                        regards, tom lane

В списке pgsql-performance по дате отправления:

Предыдущее
От: Tom Lane
Дата:
Сообщение: Re: Why does the number of rows are different in actual and estimated.
Следующее
От: Tom Lane
Дата:
Сообщение: Re: backend suddenly becomes slow, then remains slow