Message-Id: <4BE7E62C02000025000314B7@gw.wicourts.gov>
Date: Mon, 10 May 2010 10:55:40 -0500
From: "Kevin Grittner" <Kevin.Grittner@wicourts.gov>
To: "Robert Haas" <robertmhaas@gmail.com>, "Bruce Momjian" <bruce@momjian.us>
Cc: "Michael Tharp" <gxti@partiallystapled.com>,
	<pgsql-hackers@postgresql.org>,
	"Craig Ringer" <craig@postnewspapers.com.au>
Subject: Re: no universally correct setting for fsync
References: <4BE81CA1.4080201@partiallystapled.com>
	<201005101512.o4AFCZS27089@momjian.us>
	<AANLkTiktz9l00oZEjxvaMljYLebCnJQm-S9Vr4XVF071@mail.gmail.com>
In-Reply-To: <AANLkTiktz9l00oZEjxvaMljYLebCnJQm-S9Vr4XVF071@mail.gmail.com>
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Robert Haas <robertmhaas@gmail.com> wrote:
 
> "It might be safe" is a bit of a waffle.  It would be nice if we
> could provide some more clear guidance as to whether it is or is
> not, or how someone could go about testing their hardware to find
> out.
 
I think that the issue is that you could have corruption if some,
but not all, disk sectors from a page were written from OS cache to
controller cache when a failure occurred.  The window would be small
for a RAM-to-RAM write, but it wouldn't be entirely *safe* unless
there's some OS/driver environment where you could count on all the
sectors making it or none of them making it for every single page. 
Does such an environment exist?
 
-Kevin