Re: git pack/unpack over bittorrent - works!

From: Luke Kenneth Casson Leighton <luke.leighton@gmail.com>
Date: Sep 2, 2010, 19:17 UTC
Message-ID: <AANLkTi=Q7EfeUDB6PuSa88PDtaBZSMMuaMqh8hU25ECb@mail.gmail.com>
In-Reply-To: <alpine.LFD.2.00.1009021326290.19366@xanadu.home>

On Thu, Sep 2, 2010 at 6:31 PM, Nicolas Pitre <nico@fluxnic.net> wrote:

Show 15 quoted lines

> On Thu, 2 Sep 2010, A Large Angry SCM wrote:
>
>> On 09/02/2010 12:41 PM, Nicolas Pitre wrote:
>>
>> > For example, right now you already can't rely on having the exact same
>> > pack output even on the same machine using the same arguments and the
>> > same inputs simply by using threads.  As soon as you're using more than
>> > one thread (most people do these days) then your pack output becomes non
>> > deterministic.
>>
>> Finally, the real pack expert weighs in!
>
> BTW I just have a little time to quickly scan through my git mailing
> list backlog these days, and stumbled on this by luck.  So if people
> want my opinion on such matters it is safer to CC me directly.

 appreciated nicolas.  will keep it short.  ish :)

 * based on what you kindly mentioned about "git repack -f", would a
(well-written!) patch to git pack-objects to add a
"--single-thread-only" option be acceptable?

 * would you, or anyone else with enough knowledge of how this stuff
reaallly works, be willing to put some low-priority back-of-mind
thought into how to create a "canonical" pack format - one that can be
enabled with a command-line-option?  the reason i ask is because if i
even attempted such a task, i'd die of laughing (probably manically)
if it was ever accepted.  i'd rather live :)

 questions (not necessarily for nicolas) - can anyone think of any
good reasons _other_ than for multiple file-sharing to have a
"canonical" pack-object?

off the top of my head i can think of one: rsync if the transfer is interrupted. if the pack-objects are large - and not guaranteed to be the same - then an interrupted rsync transfer would be a bit of a waste of bandwidth. however if the pack-object could always be made the same, the partial transfer could carry on. musing a bit further... mmm... i supooose the same thing applies equally to http and ftp. it's a bit lame, i know: can anyone think of any better reasons?

l.