From: Jakub Narebski <jnareb@gmail.com>
To: Nicolas Pitre <nico@fluxnic.net>
Cc: Avery Pennarun <apenwarr@gmail.com>, Theodore Tso <tytso@mit.edu>,
Jeff King <peff@peff.net>, Will Palmer <wmpalmer@gmail.com>,
git@vger.kernel.org
Subject: Re: Why is "git tag --contains" so slow?
Date: Thu, 8 Jul 2010 23:20:03 +0200 [thread overview]
Message-ID: <201007082320.05017.jnareb@gmail.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1007081559300.6020@xanadu.home>
Dnia czwartek 8. lipca 2010 22:13, Nicolas Pitre napisał:
> On Thu, 8 Jul 2010, Avery Pennarun wrote:
> > On Thu, Jul 8, 2010 at 3:29 PM, Nicolas Pitre <nico@fluxnic.net> wrote:
> > > I might be looking at this from my own perspective as one of the few
> > > people who hacked extensively on the Git pack format from the very
> > > beginning. But I do see a way for the pack format to encode commit and
> > > tree objects so that walking them would be a simple lookup in the pack
> > > index file where both the SHA1 and offset in the pack for each parent
> > > can be immediately retrieved. Same for tree references. No deflating
> > > required, no binary search, just simple dereferences. And the pack size
> > > would even shrink as a side effect.
> >
> > One trick that bup uses is an additional file that sits alongside the
> > pack and acts as an index. In bup's case, this is to work around
> > deficiencies in the .idx file format when using ridiculously huge
> > numbers of objects (hundreds of millions) across a large number of
> > packfiles. But the same concept could apply here: instead of doing
> > something like rev-cache, you could just construct the "efficient"
> > part of the packv4 format (which I gather is entirely related to
> > commit messages), and store it alongside each pack.
>
> No. I want the essential information in an efficient encoding _inside_
> the pack, actually replacing the existing encoding. One of the goal is
> also to reduce repository size, not to grow it.
That's a good idea.
> > This would allow people to incrementally modify git to use the new,
> > efficient commit object storage, without breaking backward
> > compatibility with earlier versions of git. (Just as bup can index
> > huge numbers of packed objects but still stores them in the plain git
> > pack format.)
>
> Initially, what I'm aiming for is for pack-objects to produce the new
> format, for index-pack to grok it, and for sha1_file:unpack_entry() to
> simply regenerate the canonical object format whenever a pack v4 object
> is encountered. Also pack-objects would be able to revert the object
> encoding to the current format on the fly when it is serving a fetch
> request to a client which is not pack v4 aware, just like we do now with
> the ofs-delta capability.
>
> Once that stage is reached, I'll submit the lot and hope that other
> people will help incrementally converting part of Git to benefit from
> native access to the pack v4 data. The tree object walk code would be
> the first obvious candidate. And so on.
If I remember correctly with pack v4 some operations like getting size
of tree object needs encoding to current format, so they are slower than
they should be (and perhaps a bit slower than current implementation).
But that should be I think rare (well, unless one streams to
'git cat-file --batch / --batch-check').
Would pack v4 need index v4?
By the way, rev-cache project was started mainly to make "counting
objects" part of clone / fetch faster. Would pack v4 offer the same
without rev-cache?
--
Jakub Narebski
Poland
next prev parent reply other threads:[~2010-07-08 21:20 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-01 0:54 Why is "git tag --contains" so slow? Theodore Ts'o
2010-07-01 0:58 ` Shawn O. Pearce
2010-07-03 23:27 ` Sam Vilain
2010-07-01 1:00 ` Avery Pennarun
2010-07-01 12:17 ` tytso
2010-07-01 15:03 ` Jeff King
2010-07-01 15:38 ` Jeff King
2010-07-02 19:26 ` tytso
2010-07-03 8:06 ` Jeff King
2010-07-04 0:55 ` tytso
2010-07-05 12:27 ` Jeff King
2010-07-05 12:33 ` [RFC/PATCH 1/4] tag: speed up --contains calculation Jeff King
2010-10-13 22:07 ` Jonathan Nieder
2010-10-13 22:56 ` Clemens Buchacher
2011-02-23 15:51 ` Ævar Arnfjörð Bjarmason
2011-02-23 16:39 ` Jeff King
2010-07-05 12:34 ` [RFC/PATCH 2/4] limit "contains" traversals based on commit timestamp Jeff King
2010-10-13 23:21 ` Jonathan Nieder
2010-07-05 12:35 ` [RFC/PATCH 3/4] default core.clockskew variable to one day Jeff King
2010-07-05 12:36 ` [RFC/PATCH 4/4] name-rev: respect core.clockskew Jeff King
2010-07-05 12:39 ` Why is "git tag --contains" so slow? Jeff King
2010-10-14 18:59 ` Jonathan Nieder
2010-10-16 14:32 ` Clemens Buchacher
2010-10-27 17:11 ` Jeff King
2010-10-28 8:07 ` Clemens Buchacher
2010-07-05 14:10 ` tytso
2010-07-06 11:58 ` Jeff King
2010-07-06 15:31 ` Will Palmer
2010-07-06 16:53 ` tytso
2010-07-08 11:28 ` Jeff King
2010-07-08 13:21 ` Will Palmer
2010-07-08 13:54 ` tytso
2010-07-07 17:45 ` Jeff King
2010-07-08 10:29 ` Theodore Tso
2010-07-08 11:12 ` Jakub Narebski
2010-07-08 19:29 ` Nicolas Pitre
2010-07-08 19:39 ` Avery Pennarun
2010-07-08 20:13 ` Nicolas Pitre
2010-07-08 21:20 ` Jakub Narebski [this message]
2010-07-08 21:30 ` Sverre Rabbelier
2010-07-08 23:10 ` Nicolas Pitre
2010-07-08 23:15 ` Nicolas Pitre
2010-07-08 11:31 ` Jeff King
2010-07-08 14:35 ` Johan Herland
2010-07-08 19:06 ` Nicolas Pitre
2010-07-07 17:50 ` Jeff King
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