Re: clone breaks replace

From: Phillip Susi <psusi@cfl.rr.com>
Date: Jan 7, 2011, 21:44 UTC
Message-ID: <4D278930.7010100@cfl.rr.com>
In-Reply-To: <20110107205103.GC4629@burratino>

On 1/7/2011 3:51 PM, Jonathan Nieder wrote:

Show 7 quoted lines

> Phillip Susi wrote:
> 
>> Isn't the whole purpose of using replace to avoid having to use
>> filter-branch, which throws out all of the existing commit records, and
>> creates an entirely new commit chain that is slightly modified?
> 
> No.  What documentation suggested that?  Maybe it can be fixed.

It's just what made sense to me. If you can modify the history with filter-branch, then you don't need replace refs. The downside to filter-branch is that it breaks people tracking your repository, since the history they had been tracking is thrown out and replaced with a completely new commit chain that looks similar, but as far as git is concerned, is unrelated to the original. Replace refs seem to have been created to allow you to accomplish the goal of modifying an old commit record, but without having to rewrite that and all subsequent commits, causing breakage.

>  - can choose to fetch or not fetch with the usual
>    "git fetch repo refs/replace/*:refs/replace/*" syntax

It seems like this should be the default behavior. Or perhaps refs/replace should be forked into one meant to be private, and one meant to be public, and fetched by default. Or maybe it should be fetched by default, but not pushed, so you have to explicitly push replacements to the public mirror that you intend for public consumption. Having the replace only apply locally and still needing to filter-branch to make the change visible to the public seems to render the replace somewhat pointless.

Take the kernel history as an example, only imagine that Linus did not originally make that first commit leaving out the prior history, but wants to go back and fix it now. He can do it with a replace, but then if he runs filter-branch as you suggest to make the change 'real', then everyone tracking his tree will fail the next time they try to pull. You could get the same result without replace, so why bother?

If the replace was fetched by default, the people already tracking would get it the next time they pull and would not have a problem. If they wanted to see the old history, then they would already have it in the repository and just need to add --no-replace-objects to see it, or run git log on the original commit id that the replace record should refer you to ( in the comments ). Those cloning the repository for the first time would get it, and avoid fetching all of the old history since they would be using the replace record in place of the original commit.