From: Jakub Narebski <jnareb@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "Junio C Hamano" <gitster@pobox.com>, "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
Subject: Re: generation numbers
Date: Thu, 7 Jul 2011 22:10:12 +0200 [thread overview]
Message-ID: <201107072210.13254.jnareb@gmail.com> (raw)
In-Reply-To: <20110707190828.GC12044@sigill.intra.peff.net>
On Thu, 7 Jul 2011, Jeff King wrote:
> On Wed, Jul 06, 2011 at 04:22:23PM -0700, Junio C Hamano wrote:
>
> > As to the low level implementation detail I agree everything you said, but
> > I have been wondering how the generation number should intereact with
> > grafts and replaces. It certainly would be safest whenever you change
> > grafts (which should be a rare event anyway).
>
> Ugh. I hadn't even considered grafting. Yeah, grafting or replacing
> could make the generation numbers totally wrong. And not just for the
> replaced commit, but for everything that builds on top. That's perhaps
> an argument against putting them into the commit header at all; once you
> graft, everything after will have bogus generation numbers.
>
> So yeah, you would want to clear the cache any time you tweak
> replacements or grafts (which I think is what you were saying in your
> final sentence).
>
> You could do a hybrid solution, in which you have generation numbers in
> the commit header, and an external cache. You need the cache anyway to
> support older commits without the header. And then you could use the
> built-in generation numbers when there's no grafting or replacing going
> on, and the cache otherwise. That keeps the common case (no grafts)
> faster.
Or we could enhance pack protocol (new capability) to send generation
notes cache as a separate stream perhaps.
Or make generation notes cache part of post-downloading work, after
(or while) generating pack index.
> Still, if we can get the external lookup to be faster than my initial
> notes attempt (which really should not be that hard), the performance
> difference may not end up that big, and it won't even be worth putting
> them into the header at all.
I wonder if we can reuse pack index code / format somewhat.
Or perhaps some kind of on-disk hash table; we need O(1) fast lookup,
and ability to update structure 'in place'.
--
Jakub Narebski
Poland
next prev parent reply other threads:[~2011-07-07 20:10 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
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 [this message]
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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