Re: Why does this query write to the disk?

Поиск
Список
Период
Сортировка
От Kevin Grittner
Тема Re: Why does this query write to the disk?
Дата
Msg-id 48D24E6C.EE98.0025.0@wicourts.gov
обсуждение исходный текст
Ответ на Why does this query write to the disk?  ("Nikolas Everett" <nik9000@gmail.com>)
Ответы Re: Why does this query write to the disk?  (Tom Lane <tgl@sss.pgh.pa.us>)
Список pgsql-performance
>>> "Nikolas Everett" <nik9000@gmail.com> wrote:

> I'm a bit confused as to why this query writes to the disk:
> SELECT count(*)
> FROM    bigbigtable
> WHERE customerid IN (SELECT customerid FROM
> smallcustomertable)
> AND x !=
> 'special'
>
> AND y IS NULL
>
> It writes a whole bunch of data to the disk that has the tablespace
where
> bigbigtable lives as well as writes a little data to the main disk.
It
> looks like its is actually WAL logging these writes.

It's probably writing hint bits to improve performance of subsequent
access to the table.  The issue is discussed here:

http://wiki.postgresql.org/wiki/Hint_Bits

-Kevin

В списке pgsql-performance по дате отправления:

Предыдущее
От: "Nikolas Everett"
Дата:
Сообщение: Why does this query write to the disk?
Следующее
От: Tom Lane
Дата:
Сообщение: Re: Why does this query write to the disk?