From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Johannes Sixt <j6t@kdbg.org>
Cc: Junio C Hamano <gitster@pobox.com>, Nicolas Pitre <nico@cam.org>,
Nix <nix@esperi.org.uk>, Steven Grimm <koreth@midwinter.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Git Mailing List <git@vger.kernel.org>
Subject: Re: What's so special about objects/17/ ?
Date: Sun, 07 Oct 2018 21:06:13 +0200 [thread overview]
Message-ID: <87in2da862.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <f64b5c5d-ef72-a347-bd0f-7b1669a8c10d@kdbg.org>
On Sun, Oct 07 2018, Johannes Sixt wrote:
> Am 07.10.18 um 20:28 schrieb Ævar Arnfjörð Bjarmason:
>> In 2007 Junio wrote
>> (https://public-inbox.org/git/7vr6lcj2zi.fsf@gitster.siamese.dyndns.org/):
>>
>> +static int need_to_gc(void)
>> +{
>> + /*
>> + * Quickly check if a "gc" is needed, by estimating how
>> + * many loose objects there are. Because SHA-1 is evenly
>> + * distributed, we can check only one and get a reasonable
>> + * estimate.
>> + */
>
>> 1. We still have this check of objects/17/ in builtin/gc.c today. Why
>> objects/17/ and not e.g. objects/00/ to go with other 000* magic such
>> as the 0000000000000000000000000000000000000000 SHA-1? Statistically
>> it doesn't matter, but 17 seems like an odd thing to pick at random
>> out of 00..ff, does it have any significance?
>
> The reason is explained in the comment. And, BTW, you do know about
> this one: https://xkcd.com/221/ don't you? (TLDR: the title is "Random
> Number")
Picking any one number is explained in the comment. I'm asking why 17 in
particular not for correctness reasons but as a bit of historical lore,
and because my ulterior is to improve the GC docs.
The number in that comic is 4 (and no datestamp on when it was
published). Are you saying Junio's patch is somehow a reference to that
xkcd in particular, or that it's just a funny reference in this context?
>> 2. It seems overly paranoid to be checking that the files in
>> .git/objects/17/ look like a SHA-1. If we have stuff not generated by
>> git in .git/objects/??/ we probably have bigger problems than
>> prematurely triggering auto gc, can this just be removed as
>> redundant. Was this some check e.g. expecting that this would need to
>> deal with tempfiles in these directories that we created at the time
>> (but no longer do?)?
>
> It's not about that there are SHA-1s in there, it's about how many
> there are.
Right, I'm wondering if it couldn't be replaced by some general path.c
"number_of_files_in_dir" helper. I.e. why this code is being paranoid
about ignoring the likes of
.git/objects/17/{foo,bar,some-other-garbage}. A number_of_files_in_dir()
would obviously need to ignore "." and "..".
next prev parent reply other threads:[~2018-10-07 19:06 UTC|newest]
Thread overview: 97+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-09-05 7:09 People unaware of the importance of "git gc"? Linus Torvalds
2007-09-05 7:21 ` Martin Langhoff
2007-09-05 7:37 ` Karl Hasselström
2007-09-05 7:30 ` Junio C Hamano
2007-09-05 7:26 ` Tomash Brechko
2007-09-05 8:13 ` Johan Herland
2007-09-05 8:39 ` Matthieu Moy
2007-09-05 8:41 ` Johan Herland
2007-09-05 8:47 ` David Kastrup
2007-09-05 8:51 ` Pierre Habouzit
2007-09-05 9:02 ` David Kastrup
2007-09-05 9:04 ` Matthieu Moy
2007-09-05 8:51 ` Wincent Colaiuta
2007-09-05 7:42 ` Pierre Habouzit
2007-09-05 8:16 ` Junio C Hamano
2007-09-05 8:50 ` Steven Grimm
[not found] ` <86ps0xcwxo.fsf@lola.quinscape.zz>
2007-09-05 9:07 ` Steven Grimm
2007-09-05 9:13 ` David Kastrup
2007-09-05 9:07 ` Junio C Hamano
2007-09-05 9:27 ` Martin Langhoff
2007-09-05 9:33 ` Matthieu Moy
2007-09-05 14:17 ` Johan De Messemaeker
2007-09-05 17:31 ` Matthieu Moy
2007-09-05 23:56 ` Jeff King
2007-09-05 9:13 ` David Kastrup
2007-09-05 9:14 ` Pierre Habouzit
2007-09-05 17:51 ` Nix
2007-09-05 18:14 ` Steven Grimm
2007-09-05 18:22 ` Nix
2007-09-05 18:54 ` Nicolas Pitre
2007-09-05 20:01 ` Junio C Hamano
2007-09-05 20:35 ` Nicolas Pitre
2007-09-05 21:14 ` Nix
2007-09-05 21:46 ` Junio C Hamano
2007-09-05 23:04 ` Nicolas Pitre
2007-09-05 23:42 ` Junio C Hamano
2007-09-06 0:27 ` Carlos Rica
2007-09-06 5:55 ` David Kastrup
2007-09-05 21:49 ` Junio C Hamano
2007-09-05 21:59 ` Invoke "git gc --auto" from commit, merge, am and rebase Junio C Hamano
2007-09-06 2:39 ` Shawn O. Pearce
2007-09-05 20:37 ` [PATCH] Invoke "git gc --auto" from "git add" and "git fetch" Junio C Hamano
[not found] ` <69b0c0350709051357ifa547aarfe3e0b36cf9be98f@mail.gmail.com>
2007-09-05 20:59 ` Fwd: " Govind Salinas
2007-09-06 12:02 ` Johannes Schindelin
2007-09-05 21:18 ` People unaware of the importance of "git gc"? Alex Riesen
2007-09-06 2:44 ` Russ Dill
2007-09-06 2:52 ` Shawn O. Pearce
2007-09-06 9:28 ` Andreas Ericsson
2007-09-06 2:45 ` Shawn O. Pearce
2007-09-06 2:49 ` Steven Grimm
2007-09-06 2:56 ` Shawn O. Pearce
2007-09-06 15:54 ` Johannes Schindelin
2007-09-06 17:49 ` Junio C Hamano
2007-09-06 18:15 ` Linus Torvalds
2007-09-06 18:29 ` Steven Grimm
2007-09-06 23:12 ` Subject: [PATCH] git-merge-pack Junio C Hamano
2007-09-06 23:35 ` Linus Torvalds
2007-09-07 0:51 ` Nicolas Pitre
2007-09-07 1:58 ` Junio C Hamano
2007-09-07 2:32 ` Nicolas Pitre
2007-09-07 4:07 ` Shawn O. Pearce
2007-09-07 4:43 ` Junio C Hamano
2007-09-08 9:50 ` [PATCH] make sha1_file.c::matches_pack_name() available to others Junio C Hamano
2007-09-08 10:01 ` [PATCH] pack-objects --repack-unpacked Junio C Hamano
2007-09-07 7:11 ` Subject: [PATCH] git-merge-pack Johannes Sixt
2007-09-07 7:34 ` Junio C Hamano
2007-09-07 7:24 ` Andy Parkins
2007-09-07 4:48 ` People unaware of the importance of "git gc"? Shawn O. Pearce
2007-09-07 10:12 ` Johannes Schindelin
2018-10-07 18:28 ` What's so special about objects/17/ ? Ævar Arnfjörð Bjarmason
2018-10-07 18:35 ` Johannes Sixt
2018-10-07 19:06 ` Ævar Arnfjörð Bjarmason [this message]
2018-10-07 22:39 ` Johannes Sixt
2018-10-08 0:54 ` Junio C Hamano
2018-10-07 19:46 ` Junio C Hamano
2018-10-07 20:07 ` Junio C Hamano
2018-10-08 19:17 ` Stefan Beller
2018-10-09 1:03 ` Junio C Hamano
2018-10-09 17:37 ` Stefan Beller
2018-10-10 1:10 ` Junio C Hamano
2018-10-10 19:08 ` Stefan Beller
2018-10-08 10:36 ` Ævar Arnfjörð Bjarmason
2018-10-09 1:07 ` Junio C Hamano
2018-10-09 17:40 ` Stefan Beller
2007-09-05 8:16 ` People unaware of the importance of "git gc"? David Kastrup
2007-09-05 16:47 ` Govind Salinas
2007-09-05 17:19 ` Carl Worth
2007-09-05 17:55 ` Jing Xue
2007-09-05 17:35 ` Steven Grimm
2007-09-05 18:28 ` Nix
2007-09-05 17:44 ` J. Bruce Fields
2007-09-05 18:46 ` Brandon Casey
2007-09-05 19:09 ` David Kastrup
2007-09-05 19:13 ` J. Bruce Fields
2007-09-05 19:43 ` David Kastrup
2007-09-05 19:20 ` Mike Hommey
2007-09-05 21:07 ` Alex Riesen
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