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From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Stefan Beller <sbeller@google.com>, Theodore Ts'o <tytso@mit.edu>,
	git@vger.kernel.org, torvalds@linux-foundation.org
Subject: Re: [PATCH] Enable core.fsyncObjectFiles by default
Date: Tue, 23 Jun 2015 22:20:44 -0700
Message-ID: <xmqqlhf9bs2b.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <20150624033725.GA19321@peff.net> (Jeff King's message of "Tue, 23 Jun 2015 23:37:25 -0400")

Jeff King <peff@peff.net> writes:

> 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.

That matches my understanding.  IIRC, we do fsync (without a knob to
turn it off) packs, we do not fsync refs (as you described above),
the index, or working tree files (via write_entry()).  Among these:

 * If we are so paranoid that loss of new loose objects matter (as
   opposed to "Heh, it is just the matter of 'git add' again") to
   cause us to set core.fsyncObjectFiles, we should definitely fsync
   ref writes.  They are even more precious.

 * The index is much less precious.  In the worst case, you can 'git
   reset' (no flags) and re-add from the working tree and nothing
   unrecoverable is lost.  I do not mind a knob to force us fsync,
   but we may want it to be separate from core.fsyncObjectFiles.

 * The working tree files?  I am not sure.  Again, recovery is just
   to run "git diff" to notice what was eaten by the power failure
   and then "git checkout $path" to restore from a known state,
   so...

  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
2015-06-24  5:20   ` Junio C Hamano [this message]
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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