Re: seq scan over 3.3 million rows instead of single key index access

От: Andreas Kretschmer
Тема: Re: seq scan over 3.3 million rows instead of single key index access
Дата: ,
Msg-id: 20081123081339.GB7443@tux
(см: обсуждение, исходный текст)
Ответ на: seq scan over 3.3 million rows instead of single key index access  ("Andrus")
Список: pgsql-performance

Скрыть дерево обсуждения

seq scan over 3.3 million rows instead of single key index access  ("Andrus", )
 Re: seq scan over 3.3 million rows instead of single key index access  (Gregory Stark, )
  Re: seq scan over 3.3 million rows instead of single key index access  (Tom Lane, )
  Re: seq scan over 3.3 million rows instead of single key index access  ("Andrus", )
   Re: seq scan over 3.3 million rows instead of single key index access  ("A. Kretschmer", )
 Re: seq scan over 3.3 million rows instead of single key index access  (Andreas Kretschmer, )
  Re: seq scan over 3.3 million rows instead of single keyindex access  ("Andrus", )
 Re: seq scan over 3.3 million rows instead of single key index access  (Andreas Kretschmer, )

Andrus <> schrieb:

> There are  indexes on   rid(dokumnr) and dok(dokumnr) and dokumnr is int.
> Instead of using single key index, 8.1.4 scans over whole rid table.
> Sometimes idtelluued can contain more than single row so replacing join
> with equality is not possible.
>
> How to fix ?
>
> Andrus.
>
> CREATE TEMP TABLE idtellUued(dokumnr INT) ON COMMIT DROP;
> INSERT INTO idtellUued VALUES(1249228);
> explain analyze  select 1
>   from dok JOIN rid USING(dokumnr)
> JOIN idtellUued USING(dokumnr)

Try to analyse the idtellUued-table after the insert. The planner has no
knowledge that this table contains only one or e few rows, the planner
assume 1000 (iirc) in this table.


Andreas
--
Really, I'm not out to destroy Microsoft. That will just be a completely
unintentional side effect.                              (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly."   (unknown)
Kaufbach, Saxony, Germany, Europe.              N 51.05082°, E 13.56889°


В списке pgsql-performance по дате сообщения:

От: "Andrus"
Дата:
Сообщение: Re: seq scan over 3.3 million rows instead of single keyindex access
От: "Andrus"
Дата:
Сообщение: Re: Hash join on int takes 8..114 seconds