From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>,
Andreas Schwab <schwab@linux-m68k.org>,
Olaf Hering <olaf@aepfle.de>,
Git Mailing List <git@vger.kernel.org>
Subject: Re: history damage in linux.git
Date: Thu, 21 Apr 2016 10:23:10 -0700 [thread overview]
Message-ID: <CA+55aFyadCxX_Ws5fUC0QXwYYyaAjC5TC=y+tVA+YUHX1o+-iQ@mail.gmail.com> (raw)
In-Reply-To: <20160421170815.GA10783@sigill.intra.peff.net>
On Thu, Apr 21, 2016 at 10:08 AM, Jeff King <peff@peff.net> wrote:
>
> Right, because it makes the names longer. We give the second-parent
> traversal a heuristic cost. If we drop that cost to "1", like:
So I dropped it to 500 (removed the two last digits), and it gave a
reasonable answer. With 1000, it gave the same "based on 4.6" answer
as the current 65536 value does.
> which is technically true, but kind of painful to read. It may be that a
> reasonable weight is somewhere between "1" and "65535", though.
Based on my tests, the "right" number is somewhere in the 500-1000
range for this particular case. But it's still a completely made up
number.
> However, I think the more fundamental confusion with git-describe is
> that people expect the shortest distance to be the "first" tag that
> contained the commit, and that is clearly not true in a branchy history.
Yeah.
And I don't think people care *too* much, because I'm sure this has
happened before, it's just that before when it happened it wasn't
quite _so_ far off the expected path..
> I actually think most people would be happy with an algorithm more like:
>
> 1. Find the "oldest" tag (either by timestamp, or by version-sorting
> the tags) that contains the commit in question.
Yes, we might want to base the "distance" at least partly on the age
of the base commits.
> 2. Find the "simplest" path from that tag to the commit, where we
> are striving mostly for shortness of explanation, not of path (so
> "~500" is way better than "~20^2~30^2~14", even though the latter
> is technically a shorter path).
Well, so the three different paths I've seen are:
- standard git (65536), and 1000:
aed06b9 tags/v4.6-rc1~9^2~792
- non-first-parent cost: 500:
aed06b9 tags/v3.13-rc7~9^2~14^2~42
- non-first parent cost: 1:
aed06b9 tags/v3.13~5^2~4^2~2^2~1^2~42
so there clearly are multiple valid answers.
I would actually claim that the middle one is the best one - but I
claim that based on your algorithm case #1. The last one may be the
shortest actual path, but it's a shorter path to a newer tag that is a
superset of the older tag, so the middle one is actually not just
better based on age, but is a better choice based on "minimal actual
history".
Linus
next prev parent reply other threads:[~2016-04-21 17:23 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-21 11:30 history damage in linux.git Olaf Hering
2016-04-21 12:10 ` Matthieu Moy
2016-04-21 12:32 ` Olaf Hering
2016-04-21 12:51 ` Matthieu Moy
2016-04-21 13:19 ` John Keeping
2016-04-21 15:54 ` Olaf Hering
2016-04-21 16:36 ` Matthieu Moy
2016-04-21 13:24 ` Andreas Schwab
2016-04-21 16:36 ` Linus Torvalds
2016-04-21 16:59 ` Junio C Hamano
2016-04-21 17:08 ` Jeff King
2016-04-21 17:23 ` Linus Torvalds [this message]
2016-04-21 17:44 ` Stefan Beller
2016-04-21 22:16 ` Junio C Hamano
2016-04-21 18:05 ` Jeff King
2016-04-21 18:18 ` Linus Torvalds
2016-04-22 13:38 ` Johannes Schindelin
2016-04-21 17:00 ` Linus Torvalds
2016-04-21 17:23 ` Junio C Hamano
2016-04-21 17:43 ` Linus Torvalds
2016-04-21 17:59 ` Linus Torvalds
2016-04-21 18:09 ` Jeff King
2016-04-21 19:27 ` Junio C Hamano
2016-04-21 19:43 ` Linus Torvalds
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