From: "Kyle J. McKay" <mackyle@gmail.com>
To: Junio C Hamano <gitster@pobox.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: Git Mailing List <git@vger.kernel.org>
Subject: Re: Changing the default for "core.abbrev"?
Date: Thu, 29 Sep 2016 06:01:44 -0700 [thread overview]
Message-ID: <80D70A8B-0EB6-4118-8193-8D113621C57D@gmail.com> (raw)
In-Reply-To: <xmqq37knwcf4.fsf@gitster.mtv.corp.google.com>
On Sep 25, 2016, at 18:39, Linus Torvalds wrote:
> The kernel, these days, is at roughly 5 million objects, and while the
> seven hex digits are still often enough for uniqueness (and git will
> always add digits *until* it is unique), it's long been at the point
> where I tell people to do
>
> git config --global core.abbrev 12
>
> because even though git will extend the seven hex digits until the
> object name is unique, that only reflects the *current* situation in
> the repository. With 5 million objects and a very healthy growth rate,
> a 7-8 hex digit number that is unique today is not necessarily unique
> a month or two from now, and then it gets annoying when a commit
> message has a short git ID that is no longer unique when you go back
> and try to figure out what went wrong in that commit.
On Sep 25, 2016, at 20:46, Junio C Hamano wrote:
> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
>> I can just keep reminding kernel maintainers and developers to update
>> their git config, but maybe it would be a good idea to just admit
>> that
>> the defaults picked in 2005 weren't necessarily the best ones
>> possible, and those could be bumped up a bit?
>
> I am not quite sure how good any new default would be, though. Just
> like any timeout is not long enough for somebody, growing projects
> will eventually hit whatever abbreviation length they start with.
This made me curious what the situation is really like. So I crunched
some data.
Using a recent clone of $korg/torvalds/linux:
$ git rev-parse --verify d597639e203
error: short SHA1 d597639e203 is ambiguous.
fatal: Needed a single revision
So the kernel already has 11-character "short" SHA1s that are
ambiguous. Is a core.abbrev setting of 12 really good enough?
Here are the stats on the kernel's repository:
Ambiguous length 11 (but not at length 12) info:
prefixes: 2
0 (with 1 or more commit disambiguations)
Ambiguous length 10 (but not at length 11) info:
prefixes: 12
3 (with 1 or more commit disambiguations)
0 (with 2 or more commit disambiguations)
Ambiguous length 9 (but not at length 10) info:
prefixes: 186
43 (with 1 or more commit disambiguations)
1 (with 2 or more commit disambiguations)
0 (with 3 or more disambiguations)
Ambiguous length 8 (but not at length 9) info:
prefixes: 2723
651 (with 1 or more commit disambiguations)
40 (with 2 or more commit disambiguations)
1 (with 3 or more disambiguations)
maxambig: 3 (there is 1 of them)
Ambiguous length 7 (but not at length 8) info:
prefixes: 41864
9842 (with 1 or more commit disambiguations)
680 (with 2 or more commit disambiguations)
299 (with 3 or more disambiguations)
maxambig: 3 (there are 299 of them)
The "maxambig" value is the maximum number of disambiguations for any
single prefix at that prefix length. So for prefixes of length 7
there are 299 that disambiguate into 3 objects.
Just out of curiosity, generating stats on the Git repository gives:
Ambiguous length 8 (but not at length 9) info:
prefixes: 7
3 (with 1 or more commit disambiguations)
2 (with 2 or more commit disambiguations)
0 (with 3 or more disambiguations)
Ambiguous length 7 (but not at length 8) info:
prefixes: 87
36 (with 1 or more commit disambiguations)
3 (with 2 or more commit disambiguations)
0 (with 3 or more disambiguations)
Running the stats on $github/gitster/git produces some ambiguous
length 9 prefixes (one of which contains a commit disambiguation).
--Kyle
next prev parent reply other threads:[~2016-09-29 13:01 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-26 1:39 Changing the default for "core.abbrev"? Linus Torvalds
2016-09-26 3:46 ` Junio C Hamano
2016-09-26 4:34 ` Jeff King
2016-09-26 4:45 ` Junio C Hamano
2016-09-26 11:57 ` [PATCH 0/10] helping people resolve ambiguous sha1s Jeff King
2016-09-26 11:59 ` [PATCH 01/10] get_sha1: detect buggy calls with multiple disambiguators Jeff King
2016-09-26 16:37 ` Junio C Hamano
2016-09-26 17:21 ` Jeff King
2016-09-26 17:50 ` Junio C Hamano
2016-09-26 11:59 ` [PATCH 02/10] get_sha1: avoid repeating ourselves via ONLY_TO_DIE Jeff King
2016-09-26 11:59 ` [PATCH 03/10] get_sha1: propagate flags to child functions Jeff King
2016-09-26 11:59 ` [PATCH 04/10] get_short_sha1: peel tags when looking for treeish Jeff King
2016-09-26 12:11 ` Jeff King
2016-09-26 16:55 ` Junio C Hamano
2016-09-26 17:23 ` Jeff King
2016-09-26 12:00 ` [PATCH 05/10] get_short_sha1: refactor init of disambiguation code Jeff King
2016-09-26 12:00 ` [PATCH 06/10] get_short_sha1: NUL-terminate hex prefix Jeff King
2016-09-26 17:10 ` Junio C Hamano
2016-09-26 17:25 ` Jeff King
2016-09-26 17:36 ` Junio C Hamano
2016-09-26 12:00 ` [PATCH 07/10] get_short_sha1: mark ambiguity error for translation Jeff King
2016-09-26 12:00 ` [PATCH 08/10] sha1_array: let callbacks interrupt iteration Jeff King
2016-09-26 12:00 ` [PATCH 09/10] for_each_abbrev: drop duplicate objects Jeff King
2016-09-26 12:00 ` [PATCH 10/10] get_short_sha1: list ambiguous objects on error Jeff King
2016-09-26 16:36 ` Linus Torvalds
2016-09-27 5:42 ` Jacob Keller
2016-09-27 12:38 ` Jeff King
2016-09-29 13:01 ` Kyle J. McKay
2016-09-29 13:24 ` Jeff King
2016-09-29 14:36 ` Kyle J. McKay
2016-09-29 14:55 ` Jeff King
2016-09-26 17:30 ` Junio C Hamano
2016-09-26 17:34 ` Jeff King
2016-09-26 17:39 ` Junio C Hamano
2016-09-29 11:46 ` Kyle J. McKay
2016-09-29 13:03 ` Jeff King
2016-09-29 17:19 ` Junio C Hamano
2016-09-30 5:51 ` Jacob Keller
2019-02-04 16:12 ` [RFC/PATCH] core.abbrev doc: document and test the abbreviation length Ævar Arnfjörð Bjarmason
2019-02-04 19:13 ` Junio C Hamano
2019-02-04 20:04 ` Junio C Hamano
2019-02-04 21:36 ` Ævar Arnfjörð Bjarmason
2019-02-04 23:32 ` Jeff King
2019-02-04 23:50 ` Ævar Arnfjörð Bjarmason
2019-02-06 18:29 ` Jeff King
2019-02-06 18:36 ` Ævar Arnfjörð Bjarmason
2016-09-26 6:33 ` Changing the default for "core.abbrev"? Matthieu Moy
2016-09-26 12:09 ` Jeff King
2016-09-29 13:01 ` Kyle J. McKay [this message]
2016-09-26 7:13 ` Christian Couder
2016-09-28 23:30 ` [PATCH 0/4] raising core.abbrev default to 12 hexdigits Junio C Hamano
2016-09-28 23:30 ` [PATCH 1/4] config: allow customizing /etc/gitconfig location Junio C Hamano
2016-09-29 9:53 ` Jakub Narębski
2016-09-29 17:20 ` Junio C Hamano
2016-09-29 17:45 ` Matthieu Moy
2016-09-28 23:30 ` [PATCH 2/4] t13xx: do not assume system config is empty Junio C Hamano
2016-09-29 9:01 ` Jeff King
2016-09-29 18:13 ` Junio C Hamano
2016-09-29 18:26 ` Jeff King
2016-09-29 18:57 ` Junio C Hamano
2016-09-29 19:18 ` Jeff King
2016-09-29 19:57 ` Junio C Hamano
2016-09-29 19:06 ` Junio C Hamano
2016-09-29 19:26 ` Jeff King
2016-09-29 21:03 ` Junio C Hamano
2016-09-29 21:08 ` Jeff King
2016-09-28 23:30 ` [PATCH 3/4] worktree: honor configuration variables Junio C Hamano
2016-09-28 23:30 ` [PATCH 4/4] core.abbrev: raise the default abbreviation to 12 hexdigits Junio C Hamano
2016-09-29 2:44 ` SZEDER Gábor
2016-09-29 5:27 ` Lukas Fleischer
2016-09-29 9:22 ` Jeff King
2016-09-29 9:15 ` Jeff King
2016-09-29 10:03 ` Matthieu Moy
2016-09-29 12:52 ` SZEDER Gábor
2016-09-29 5:58 ` Johannes Sixt
2016-09-29 18:05 ` Junio C Hamano
2016-09-29 18:37 ` Linus Torvalds
2016-09-29 18:55 ` Linus Torvalds
2016-09-29 19:06 ` Linus Torvalds
2016-09-29 19:42 ` Junio C Hamano
2016-09-30 0:56 ` Mike Hommey
2016-09-30 1:01 ` Linus Torvalds
2016-09-30 19:41 ` Ævar Arnfjörð Bjarmason
2016-09-29 19:16 ` Jeff King
2016-09-29 19:40 ` Linus Torvalds
2016-09-29 19:45 ` Junio C Hamano
2016-09-29 21:53 ` Linus Torvalds
2016-09-29 23:13 ` Junio C Hamano
2016-09-29 23:20 ` Junio C Hamano
2016-09-30 0:20 ` Linus Torvalds
2016-09-30 0:28 ` Linus Torvalds
2016-09-30 0:57 ` Linus Torvalds
2016-09-30 1:18 ` Linus Torvalds
2016-09-30 3:54 ` Junio C Hamano
2016-09-30 4:10 ` Junio C Hamano
2016-09-30 4:18 ` Linus Torvalds
2016-09-30 4:29 ` Linus Torvalds
2016-09-30 4:27 ` Junio C Hamano
2016-09-30 4:35 ` Junio C Hamano
2016-09-30 18:40 ` Junio C Hamano
2016-09-30 18:51 ` Linus Torvalds
2016-09-30 19:00 ` Junio C Hamano
2016-09-30 4:11 ` Linus Torvalds
2016-09-30 8:06 ` Jeff King
2016-09-30 17:54 ` Linus Torvalds
2016-09-30 18:05 ` Jeff King
2016-09-30 18:21 ` Linus Torvalds
2016-09-30 20:01 ` Junio C Hamano
2016-09-30 17:56 ` Junio C Hamano
2016-09-30 7:47 ` Jeff King
2016-09-29 9:25 ` Jeff King
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