Re: 'git replace' and pushing

[Cory Fields <FOSS@AtlasTechnologiesInc.com>]

On Thu, Nov 25, 2010 at 3:37 AM, Michael J Gruber
<git@drmicha.warpmail.net> wrote:
> Cory Fields venit, vidit, dixit 24.11.2010 05:33:
>> I am having some trouble understanding how a replaced object (commit)
>> should behave when pushed to a remote repo. Here's my scenario:
>>
>> We are moving from svn to git. Our svn repo is huge, and most of the
>> history is useless. To save space, I would like to do a 50/50 split so
>> that when the repo is cloned, 50% is seen by default, and the
>> historical 50% can be seen by fetching the replacement history. I've
>> done this by creating a phony snapshot at 3 then using a 'replace' to
>> put the others on top. The history is purely linear.
>>
>> 1---2---3---4---5
>>                  \---4---5
>
> I assume the "other" 4 goes off 3 (you're not using a monospaced font,
> are you?).
>

I used a monospace font, but gmail decided not to use it. Sorry for that.

> Also, the other 4 should have no parent, otherwise you've not cut-off
> any history.

I created a "fake" 4 that consists of the full working tree at 4 with no parent.
As I mentioned, everything looks fine locally.

>
>>
>> When the replacement is in place, the repo is half size (commit-wise)
>> as expected. The problem is that 'git push' does not honor the
>> replace. So when I push, all objects go with it, which defeats the
>> purpose. The only way that seams to work is doing a filter-branch and
>> replacing the other way.
>>
>> Is this by design? I would really like a way to split the repo without
>> breaking hashes for the developers that have already begun using git
>> svn.
>
> It is by design since a replace creates a "fake history", and this
> should not be created behind a users back.
>
> The 5 is not rewritten, and it's ancestry contains the whole history. If
> that is the commit your developers have already and that you want to
> preserve then there's not much you can do.
>
> You could try to push or pull your replacement refs first (refs/replace)
> but I don't think this will change what objects the push of 5 will
> transfer. Just have a try.

I tried this to no avail.

I realize that allowing replacements to be pushed "behind users backs", so
I guess not respecting it makes sense.

But is there no way that I can pull this off without rewriting hashes?

Thanks,
Cory