Re: Figured out how to get Mozilla into git

From: Jakub Narebski <jnareb@gmail.com>
Date: Jun 10, 2006, 08:21 UTC
Message-ID: <e6dvds$oes$1@sea.gmane.org>
In-Reply-To: <Pine.LNX.4.64.0606092001590.5498@g5.osdl.org>

Linus Torvalds wrote:

Show 26 quoted lines

> On Fri, 9 Jun 2006, Carl Worth wrote:
> 
>> On Fri, 9 Jun 2006 22:21:17 -0400, "Jon Smirl" wrote:
>> > 
>> > Could you clone the repo and delete changesets earlier than 2004? Then
>> > I would clone the small repo and work with it. Later I decide I want
>> > full history, can I pull from a full repository at that point and get
>> > updated? That would need a flag to trigger it since I don't want full
>> > history to come over if I am just getting updates from someone else's
>> > tree that has a full history.
>> 
>> This is clearly a desirable feature, and has been requested by several
>> people (including myself) looking to switch some large-ish histories
>> from an existing system to git.
> 
> The thing is, to some degree it's really fundamentally hard.
> 
> It's easy for a linear history. What you do for a linear history is to 
> just get the top commit, and the tree associated with it, and then you 
> cauterize the parent by just grafting it to go away. Boom. You're done.
> 
> The problems are that if the preceding history _wasn't_ linear (or, in 
> fact, _subsequent_ development refers to it by having branched off at an 
> earlier point), and you try to pull your updates, the other end (that 
> knows about all the history) will assume you have all the history that you 
> don't have, and will send you a pack assuming that.

Couldn't it be solved by enhancing initial handshake to send from puller (object receivier) to pullee (object sender) the contents of graft file, or better the contents of cauterizing graft file - without splitting graft file we better have an option to send graft file or not, when graft file is used to join historical repository line of development not to cauterize history.

Then the sender would use sent cauterizing history graft file for calculating which objects to sedn _only_, "in memory" cauterizing it's own history.

Main disadvantage is if one cauterized history too eagerly, and shallow clone history can lack merge bases, and have no way to get them _simply_ using this approach...

Now I guess you would tell me why this very simple idea is stupid...

-- 
Jakub Narebski
Warsaw, Poland
ShadeHawk on #git