To: pgsql-hackers@postgresql.org
Subject: Re: Sync vs. fsync during checkpoint
References: <200401301701.i0UH1bZ08600@candle.pha.pa.us>
In-Reply-To: <200401301701.i0UH1bZ08600@candle.pha.pa.us>
From: Greg Stark <gsstark@mit.edu>
Organization: The Emacs Conspiracy; member since 1992
Date: 02 Feb 2004 17:43:07 -0500
Message-ID: <87ptcxumpw.fsf@stark.xeocode.com>
Lines: 21
User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii

Bruce Momjian <pgman@candle.pha.pa.us> writes:

> As some know, win32 doesn't have sync, and some are concerned that sync
> isn't reliable enough during checkpoint anyway.
> 
> The trick is to somehow record all files modified since the last
> checkpoint, and open/fsync/close each one.

Note that some people believe that if you do this it doesn't guarantee that
any data written to other file descriptors referring to the same files would
also get synced.

I am not one of those people however. Both Solaris and NetBSD kernel hackers
have told me those OS's would work in such a scheme and furthermore that they
cannot imagine any sane VFS that would fail.

I definitely think it's better than calling sync(2) which doesn't guarantee
the blocks are written by any particular time at all..

-- 
greg