From: Theodore Ts'o <tytso@mit.edu>
To: Junio C Hamano <gitster@pobox.com>
Cc: Stefan Beller <sbeller@google.com>,
git@vger.kernel.org, peff@peff.net,
torvalds@linux-foundation.org
Subject: Re: [PATCH] Enable core.fsyncObjectFiles by default
Date: Wed, 24 Jun 2015 10:30:07 -0400 [thread overview]
Message-ID: <20150624143007.GC14324@thunk.org> (raw)
In-Reply-To: <xmqqegl1brjb.fsf@gitster.dls.corp.google.com>
On Tue, Jun 23, 2015 at 10:32:08PM -0700, Junio C Hamano wrote:
>
> Regarding loose object files, given that we write to a temporary,
> optionally fsync, close and then move to the final name, would we
> still see partially written file if we omit the fsync, or would the
> corruption be limited to either empty or missing?
*Most* of the time the corruption will be an empty or missing file.
It's possible that the file could be partially written. This is a
relatively low-probability event, with the probability going up if the
object file is large, and/or if the system is under memory pressure.
> The reason I am wondering is because the codepath to create an
> object (i.e. "update-index --add", "hash-object -w", or "add") first
> checks if a packed or a loose object file _exists_ and if so
> bypasses writing the same thing anew, but the existence check for a
> loose object is to merely making sure that access(F_OK) (and
> optionally utime()) succeeds. If the potential breakage is limited
> to truncation to empty, then we could replace it with stat(2) and
> st.st_size check, as no loose object file can be empty.
It would certainly be a good thing to do a st_size check; it can't
possible hurt, and it will catch a large number of failures after a
power failure. I could also imagine some hueristics that force an
fsync if the object file is larger than a certain size (say, 4k if you
are very paranoid, a few hundred kilobytes if you are less so), but
past a certain point, it might be better just to tell the user to use
fsyncObjectFiles and be done with it.
- Ted
next prev parent reply other threads:[~2015-06-24 14:30 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-23 21:57 [PATCH] Enable core.fsyncObjectFiles by default 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 [this message]
2015-06-24 1:07 ` Duy Nguyen
2015-06-24 3:37 ` Jeff King
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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