From: A Large Angry SCM <gitzilla@gmail.com>
To: Luke Kenneth Casson Leighton <luke.leighton@gmail.com>
Cc: Nguyen Thai Ngoc Duy <pclouds@gmail.com>, git <git@vger.kernel.org>
Subject: Re: git pack/unpack over bittorrent - works!
Date: Thu, 02 Sep 2010 12:58:14 -0400 [thread overview]
Message-ID: <4C7FD7A6.9090402@gmail.com> (raw)
In-Reply-To: <AANLkTikBnKQJmgOms2wK1+6fCLtHWiWkhuCVMN7kKLXP@mail.gmail.com>
On 09/02/2010 11:42 AM, Luke Kenneth Casson Leighton wrote:
> On Thu, Sep 2, 2010 at 4:33 PM, A Large Angry SCM<gitzilla@gmail.com> wrote:
>> On 09/02/2010 09:37 AM, Luke Kenneth Casson Leighton wrote:
>>>
>>> On Wed, Sep 1, 2010 at 11:04 PM, Nguyen Thai Ngoc Duy<pclouds@gmail.com>
>>> wrote:
>>
>> [...]
>>>>
>>>> There were discussions whether a pack is stable enough to
>>>> be shared like this,
>>>
>>> it seems to be. as long as each version of git produces the exact
>>> same pack object, off of the command "git pack-objects --all --stdout
>>> --thin {ref}< {objref}"
>>
>> This is not guaranteed.
>
> ok. greeeat.
>
> so, some sensible questions:
>
> * what _can_ be guaranteed?
>
> * diffs?
Given a pre-image and a post-image, the diff/delta created will recreate
the post-image from the pre-image. The bit level representation of the
diff/delta is not guaranteed.
> * git-format-patches? (which i am aware can do binary files and also
> rms)?
See above.
> * individual files in the .git/objects directory?
Uncompressed: yes. Compressed: no.
> and, asking perhaps some silly questions:
>
> * why is it not guaranteed?
The pack format was created to move objects from one repository to
another. To do that efficiently, it uses many heuristics to decide how
much information is _sufficient_ to do the job but but leaves it to the
implementation and user to decide the various trade offs. For instance,
there is no canonical the order of the object information in a pack or
that the pack must be minimal. This also allows for the multi-threaded
pack implementation.
> * under what circumstances is it not guaranteed? and, crucially, is
> it necessary to care? i.e. if someone does a shallow git clone, i
> couldn't give a stuff.
Pretty much all of the time.
> * is it possible to _make_ the repository guaranteed to produce
> identical pack objects?
Identical code on identical systems with identical repositories without
multi-threading _might_ work.
> * does for example "git gc" change the object store in such a way such
> that one git repo will produce a different pack-object from the same
> ref? if so, can running "git gc" prior to producing the pack-objects
> gurantee that the pack-objects will be the same?
See above.
> * is it a versioning issue? is it because there are different
> versions (2 and 3)? if so, that's ok, you just force people to use
> the same pack-object versions.
No.
> etc. etc.
>
> l.
>
next prev parent reply other threads:[~2010-09-02 16:58 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-09-01 14:36 git pack/unpack over bittorrent - works! Luke Kenneth Casson Leighton
2010-09-01 22:04 ` Nguyen Thai Ngoc Duy
2010-09-02 13:37 ` Luke Kenneth Casson Leighton
2010-09-02 13:53 ` Luke Kenneth Casson Leighton
2010-09-02 14:08 ` Ævar Arnfjörð Bjarmason
2010-09-02 15:33 ` A Large Angry SCM
2010-09-02 15:42 ` Luke Kenneth Casson Leighton
2010-09-02 15:51 ` Luke Kenneth Casson Leighton
2010-09-02 17:06 ` A Large Angry SCM
2010-09-02 15:58 ` Jeff King
2010-09-02 16:41 ` Nicolas Pitre
2010-09-02 17:09 ` A Large Angry SCM
2010-09-02 17:31 ` Nicolas Pitre
2010-09-02 19:17 ` Luke Kenneth Casson Leighton
2010-09-02 19:29 ` Shawn O. Pearce
2010-09-02 19:51 ` Luke Kenneth Casson Leighton
2010-09-02 20:06 ` Luke Kenneth Casson Leighton
2010-09-03 0:36 ` Nicolas Pitre
2010-09-03 10:34 ` Luke Kenneth Casson Leighton
2010-09-03 17:03 ` Junio C Hamano
2010-09-02 20:28 ` Brandon Casey
2010-09-02 20:48 ` Luke Kenneth Casson Leighton
2010-09-02 20:45 ` Jakub Narebski
2010-09-02 21:10 ` Luke Kenneth Casson Leighton
2010-09-02 21:19 ` Luke Kenneth Casson Leighton
2010-09-03 0:29 ` Nicolas Pitre
2010-09-03 2:48 ` Nguyen Thai Ngoc Duy
2010-09-03 10:55 ` Luke Kenneth Casson Leighton
2010-09-03 10:23 ` Luke Kenneth Casson Leighton
2010-09-03 10:54 ` Luke Kenneth Casson Leighton
2010-09-02 18:07 ` Luke Kenneth Casson Leighton
2010-09-02 18:23 ` Casey Dahlin
2010-09-02 16:58 ` A Large Angry SCM [this message]
2010-09-02 17:21 ` Nicolas Pitre
2010-09-02 19:41 ` Luke Kenneth Casson Leighton
2010-09-02 19:52 ` A Large Angry SCM
2010-09-02 23:09 ` Nicolas Pitre
2010-09-03 10:37 ` Theodore Tso
2010-09-03 11:04 ` Luke Kenneth Casson Leighton
2010-09-03 17:12 ` Junio C Hamano
2010-09-03 18:31 ` Ted Ts'o
2010-09-03 19:41 ` Nicolas Pitre
2010-09-03 21:11 ` Luke Kenneth Casson Leighton
2010-09-04 0:24 ` Nguyen Thai Ngoc Duy
2010-09-04 0:57 ` Nguyen Thai Ngoc Duy
2010-09-04 1:52 ` Artur Skawina
2010-09-04 4:39 ` Nicolas Pitre
2010-09-04 5:42 ` Artur Skawina
2010-09-04 6:13 ` Nicolas Pitre
2010-09-04 11:58 ` Luke Kenneth Casson Leighton
2010-09-04 13:14 ` Luke Kenneth Casson Leighton
2010-09-05 2:16 ` Nicolas Pitre
2010-09-05 18:05 ` Luke Kenneth Casson Leighton
2010-09-05 23:52 ` Nicolas Pitre
2010-09-06 13:23 ` Luke Kenneth Casson Leighton
2010-09-06 16:51 ` Nicolas Pitre
2010-09-06 22:33 ` Luke Kenneth Casson Leighton
2010-09-06 23:34 ` Junio C Hamano
2010-09-06 23:57 ` Nicolas Pitre
2010-09-07 0:17 ` Luke Kenneth Casson Leighton
2010-09-07 0:29 ` Luke Kenneth Casson Leighton
2010-09-04 13:42 ` Artur Skawina
[not found] ` <20100904155638.GA17606@pcpool00.mathematik.uni-freiburg.de>
2010-09-04 17:23 ` Artur Skawina
2010-09-04 18:46 ` Artur Skawina
2010-09-04 1:57 ` Theodore Tso
2010-09-04 5:23 ` Kyle Moffett
2010-09-04 11:46 ` Theodore Tso
2010-09-04 14:06 ` Luke Kenneth Casson Leighton
2010-09-05 1:32 ` Nicolas Pitre
2010-09-05 17:16 ` Luke Kenneth Casson Leighton
2010-09-04 5:40 ` Nicolas Pitre
2010-09-04 12:00 ` Theodore Tso
2010-09-04 12:44 ` Luke Kenneth Casson Leighton
2010-09-04 14:50 ` Luke Kenneth Casson Leighton
2010-09-04 18:14 ` Ted Ts'o
2010-09-04 20:00 ` Luke Kenneth Casson Leighton
2010-09-04 22:41 ` Ted Ts'o
2010-09-05 17:22 ` Luke Kenneth Casson Leighton
2010-09-04 20:20 ` Jakub Narebski
2010-09-04 20:47 ` Luke Kenneth Casson Leighton
2010-09-04 21:16 ` Jakub Narebski
2010-09-04 21:24 ` Luke Kenneth Casson Leighton
2010-09-04 22:47 ` Ted Ts'o
2010-09-05 1:43 ` Tomas Carnecky
2010-09-05 1:18 ` Nicolas Pitre
2010-09-05 17:25 ` Luke Kenneth Casson Leighton
2010-09-06 0:05 ` Nicolas Pitre
2010-09-04 12:33 ` Luke Kenneth Casson Leighton
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