Re: 'git replace' and pushing

From: Cory Fields <foss@atlastechnologiesinc.com>
Date: Nov 27, 2010, 01:58 UTC
Message-ID: <AANLkTi=FjSFLsbXf2Rp_Onm26yyxX+xSPrh2pB=_f5RU@mail.gmail.com>
In-Reply-To: <7vvd3jptch.fsf@alter.siamese.dyndns.org>

On Fri, Nov 26, 2010 at 6:18 PM, Junio C Hamano <gitster@pobox.com> wrote:

Show 29 quoted lines

> Jonathan Nieder <jrnieder@gmail.com> writes:
>
>>  Real history
>>  ------------
>>  4' --- 5 --- 6
>>
>>  1 --- 2 --- 3 --- 4
>>
>>  Fake history
>>  ------------
>>  1 --- 2 --- 3 --- 4 --- 5 --- 6
>>
>>  Replacement ref
>>  ---------------
>>  4' --> 4
>>
>> This way, a person a person can fetch either piece of real history
>> without trouble, and if they fetch the replacement ref, too, the
>> history is pasted together.
>>
>> It is not possible in git to push a commit without its ancestors;
>> replacement refs do not change that.
>
> True, but I suspect the above picture pretty much satisfies Cory's initial
> wish, no?  You can fetch recent 4'--5---6 history as if 4' were the root
> commit, and if you fetched replacement that tells us to pretend that 4'
> has 3 as its parent (and the history leading to 3), you will get a deeper
> history.
>

Yes, both of these can be accomplished. I've managed to get that part working, where a default clone pulls in half history, and fetching refs/replace gives you the rest. The only problem is that it requires a filter-branch before pushing. Otherwise, 4 gets pushed rather than 4', meaning that clones will require all the objects. So it works, but I'll have to spend quite a while making it 'perfect' so that I only have to rewrite history once.

A shallow clone does not fit for us, because we want the default clone to only pull half. Having a public 1gb repository that will be cloned quite often is bound to make our host unhappy, so we're doing everything we can to get the size down.

Also, maybe I haven't made this clear... the "real" commit IDs need to match the "fake" ones in order to prevent confusion. I think that's the part that makes this so difficult. Otherwise, something like this [1] would work just fine (probably exactly what Junio was suggesting)

Any other suggestions? Or do I just have to face the fact that I'm going to have to break hashes?

[1] http://progit.org/2010/03/17/replace.html

Cory