From: Jakub Narebski <jnareb@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "Ted Ts'o" <tytso@mit.edu>,
"Jonathan Nieder" <jrnieder@gmail.com>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
"Clemens Buchacher" <drizzd@aon.at>,
git@vger.kernel.org, "Junio C Hamano" <gitster@pobox.com>
Subject: Re: generation numbers (was: [PATCH 0/4] Speed up git tag --contains)
Date: Wed, 6 Jul 2011 20:46:42 +0200 [thread overview]
Message-ID: <201107062046.43820.jnareb@gmail.com> (raw)
In-Reply-To: <20110706181200.GD17978@sigill.intra.peff.net>
On Wed, 6 Jul 2011, Jeff King wrote:
> On Wed, Jul 06, 2011 at 11:01:03AM -0400, Ted Ts'o wrote:
>
> > Is it worth it to try to replicate this information across repositories?
>
> Probably not. I suggested notes-cache just because the amount of code is
> very trivial.
Well, generation numbers are universal and would help everybody. For
new commits with 'generation' header those would be always replicated,
for old commits with 'generation' notes / notes-cache the can be
replicated.
> One problem with notes storage is that it's not well optimized for tiny
> pieces of data like this (e.g., the generation number should fit in a
> 32-bit unsigned int, as its max is the size of the longest single path
> in the history graph). But notes are much more general; we will actually
> map each commit to a blob object containing the generation number, which
> is pretty wasteful.
Wasn't textconv-cache using commit-less notes? The same can be done
for generation notes-cache. Though it is still wasteful... By the
way, would we be using text representation (like in 'generation'
commit header) or 32-bit integer binary representation in some
ordering, or variable-length integer (I think git uses them somewhere)?
Nb. I wonder if 32-bit unsigned int would always be enough, for example
Linux kernel + history.
> > Why not just simply have a cache file in the git directory which is
> > managed somewhat like gitk.cache; call it generation.cache?
>
> Yeah, that would be fine. With a sorted list of binary sha1s and 32-bit
> generation numbers, you're talking about 24 bytes per commit. Or a 6
> megabyte cache for linux-2.6.
>
> You'd probably want to be a little clever with updates. If I have
> calculated the generation number of every commit, and then do "git
> commit; git tag --contains HEAD", you probably don't want to rewrite the
> entire cache. You could probably journal a fixed number of entries in an
> unsorted file (or even in a parallel directory structure to loose
> objects), and then periodically write out the whole sorted list when the
> journal gets too big. Or choose a more clever data structure that can do
> in-place updates.
And that is the difference between gitk.cache (generated _once_ when starting
gitk, and regenerated on request), and idea of generation.cache
I think it would be simpler to use generation header + generation notes.
Or start with generation notes only.
--
Jakub Narebski
Poland
next prev parent reply other threads:[~2011-07-06 18:46 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-11 19:04 [PATCH 0/4] Speed up git tag --contains Ævar Arnfjörð Bjarmason
2011-06-11 19:04 ` [PATCH 1/4] tag: speed up --contains calculation Ævar Arnfjörð Bjarmason
2011-06-11 19:04 ` [PATCH 2/4] limit "contains" traversals based on commit timestamp Ævar Arnfjörð Bjarmason
2011-06-11 19:04 ` [PATCH 3/4] default core.clockskew variable to one day Ævar Arnfjörð Bjarmason
2011-06-11 19:04 ` [PATCH 4/4] Why is "git tag --contains" so slow? Ævar Arnfjörð Bjarmason
2011-07-06 6:40 ` [PATCH 0/4] Speed up git tag --contains Jeff King
2011-07-06 6:54 ` Jeff King
2011-07-06 19:06 ` Clemens Buchacher
2011-07-06 6:56 ` Jonathan Nieder
2011-07-06 7:03 ` Jeff King
2011-07-06 14:26 ` generation numbers (was: [PATCH 0/4] Speed up git tag --contains) Jakub Narebski
2011-07-06 15:01 ` Ted Ts'o
2011-07-06 18:12 ` Jeff King
2011-07-06 18:46 ` Jakub Narebski [this message]
2011-07-07 18:59 ` Jeff King
2011-07-07 19:34 ` generation numbers Junio C Hamano
2011-07-07 20:31 ` Jakub Narebski
2011-07-07 20:52 ` A Large Angry SCM
2011-07-08 0:29 ` Junio C Hamano
2011-07-08 22:57 ` Jeff King
2011-07-06 23:22 ` Junio C Hamano
2011-07-07 19:08 ` Jeff King
2011-07-07 20:10 ` Jakub Narebski
2018-01-12 18:56 ` [PATCH 0/4] Speed up git tag --contains csilvers
2018-03-03 5:15 ` Jeff King
2018-03-08 23:05 ` csilvers
2018-03-12 13:45 ` Derrick Stolee
2018-03-12 23:59 ` Jeff King
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