From: | Joost Kraaijeveld <J(dot)Kraaijeveld(at)Askesis(dot)nl> |
---|---|
To: | PFC <lists(at)peufeu(dot)com> |
Cc: | David Lang <david(at)lang(dot)hm>, Richard Huxton <dev(at)archonet(dot)com>, pgsql-performance(at)postgresql(dot)org |
Subject: | Re: x206-x225 |
Date: | 2006-03-11 14:26:14 |
Message-ID: | 1142087174.6634.32.camel@localhost |
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Lists: | pgsql-performance |
On Sat, 2006-03-11 at 12:33 +0100, PFC wrote:
> >> each transaction requires a sync to the disk, a sync requires a real
> >> write (which you then wait for), so you can only do one transaction per
> >> rotation.
> > Not according to a conversation I had with Western Digital about the
>
>
> It depends if you consider that "written to the disk" means "data is
> somewhere between the OS cache and the platter" or "data is writter on the
> platter and will survive a power loss".
>
> Postgres wants the second option, of course.
I assume that for PostgreSQL "written to disk" is after fsync returned
successfully. In practice that could very well mean that the data is
still in a cache somewhere (controller or harddisk, not in the OS
anymore, see also man page of fsync)
--
Groeten,
Joost Kraaijeveld
Askesis B.V.
Molukkenstraat 14
6524NB Nijmegen
tel: 024-3888063 / 06-51855277
fax: 024-3608416
e-mail: J(dot)Kraaijeveld(at)Askesis(dot)nl
web: www.askesis.nl
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