Re: PostgreSQL runs a query much slower than BDE and MySQL

Поиск
Список
Период
Сортировка
От Tom Lane
Тема Re: PostgreSQL runs a query much slower than BDE and MySQL
Дата
Msg-id 5321.1155820310@sss.pgh.pa.us
обсуждение исходный текст
Ответ на Re: PostgreSQL runs a query much slower than BDE and MySQL  ("Peter Hardman" <peter@ssbg.zetnet.co.uk>)
Ответы Re: PostgreSQL runs a query much slower than BDE and  (Mark Lewis <mark.lewis@mir3.com>)
Re: PostgreSQL runs a query much slower than BDE and MySQL  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-performance
"Peter Hardman" <peter@ssbg.zetnet.co.uk> writes:
> I wonder whether Paradox and MySQL are just not doing the sort (this
> seems to be what eats up the time), since the output of the subquery
> is in fact already in the proper order.

MSSQL (from the other thread).  I feel fairly safe in assuming that
MySQL's query optimizer is not nearly in the league to do this query
effectively.  (I like the theory Arjen mentioned that what you are
measuring there is the effects of their query cache rather than a
smart fundamental implementation.)  I wonder whether MSSQL has an
EXPLAIN equivalent ...

Anywy, your point about the sort being redundant is a good one, and
offhand I'd have expected PG to catch that; I'll have to look into
why it didn't.  But that's not going to explain a 10x speed
difference, because the sort isn't 90% of the runtime.

            regards, tom lane

В списке pgsql-performance по дате отправления:

Предыдущее
От: Markus Schaber
Дата:
Сообщение: Re: PostgreSQL runs a query much slower than BDE and MySQL
Следующее
От: Mark Lewis
Дата:
Сообщение: Re: PostgreSQL runs a query much slower than BDE and