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From: Jeff King <peff@peff.net>
To: Stefan Beller <sbeller@google.com>
Cc: Theodore Ts'o <tytso@mit.edu>,
	git@vger.kernel.org, gitster@pobox.com,
	torvalds@linux-foundation.org
Subject: Re: [PATCH] Enable core.fsyncObjectFiles by default
Date: Tue, 23 Jun 2015 23:37:25 -0400
Message-ID: <20150624033725.GA19321@peff.net> (raw)
In-Reply-To: <1435096643-18159-1-git-send-email-sbeller@google.com>

On Tue, Jun 23, 2015 at 02:57:23PM -0700, Stefan Beller wrote:

> Linus Torvalds started a discussion[1] if we want to play rather safe
> than use defaults which make sense only for the most power users of Git:
> 
> > So git is "safe" in the sense that you won't really lose any data,
> > but you may well be inconvenienced.  The "fsync each object" config
> > option is there in case you don't want that inconvenience, but it
> > should be noted that it can make for a hell of a performance impact.
> 
> > Of course, it might well be the case that the actual default
> > might be worth turning around. Most git users probably don't
> > care about that kind of "apply two hundred patches from Andrew
> > Morton" kind of workload, although "rebase a big patch-series"
> > does end up doing basically the same thing, and might be more
> > common.
> 
> This patch enables fsync_object_files by default.

If you are looking for safety out of the box, I think this falls far
short, as we do not fsync all of the other files. For instance, we do
not fsync refs before they are written (nor anything else that uses the
commit_lock_file() interface to rename, such as the index).  We do
always fsync packfiles and their indices.

I had always assumed this was fine on ext4 with data=ordered (i.e.,
either the rename and its pointed-to content will go through, or not; so
you either get your update or the old state, but not a garbage or empty
file). But it sounds from what Ted wrote in:

  http://article.gmane.org/gmane.linux.file-systems/97255

that this may not be the case. If it's not, I think we should consider
fsyncing ref writes.

-Peff

  parent reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-06-23 21:57 Stefan Beller
2015-06-23 22:21 ` Junio C Hamano
2015-06-23 23:29   ` Theodore Ts'o
2015-06-24  5:32     ` Junio C Hamano
2015-06-24 14:30       ` Theodore Ts'o
2015-06-24  1:07 ` Duy Nguyen
2015-06-24  3:37 ` Jeff King [this message]
2015-06-24  5:20   ` Junio C Hamano
2018-01-17 18:48 [PATCH] enable " Christoph Hellwig
2018-01-17 19:04 ` Junio C Hamano
2018-01-17 19:35   ` Christoph Hellwig
2018-01-17 20:05     ` Andreas Schwab
2018-01-17 19:37   ` Matthew Wilcox
2018-01-17 19:42     ` Christoph Hellwig
2018-01-17 21:44   ` Ævar Arnfjörð Bjarmason
2018-01-17 22:07     ` Linus Torvalds
2018-01-17 22:25       ` Linus Torvalds
2018-01-17 23:16       ` Ævar Arnfjörð Bjarmason
2018-01-17 23:42         ` Linus Torvalds
2018-01-17 23:52       ` Theodore Ts'o
2018-01-17 23:57         ` Linus Torvalds
2018-01-18 16:27           ` Christoph Hellwig
2018-01-19 19:08             ` Junio C Hamano
2018-01-20 22:14               ` Theodore Ts'o
2018-01-20 22:27                 ` Junio C Hamano
2018-01-22 15:09                   ` Ævar Arnfjörð Bjarmason
2018-01-22 18:09                     ` Theodore Ts'o
2018-01-23  0:47                       ` Jeff King
2018-01-23  5:45                         ` Theodore Ts'o
2018-01-23 16:17                           ` Jeff King
2018-01-23  0:25                     ` Jeff King
2018-01-21 21:32             ` Chris Mason
2020-09-17 11:06         ` Ævar Arnfjörð Bjarmason
2020-09-17 14:14           ` Christoph Hellwig
2020-09-17 15:30           ` Junio C Hamano
2018-01-17 20:55 ` Jeff King
2018-01-17 21:10   ` Christoph Hellwig

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