Split project without change duplication

[Daniil Gan’kov]

Hello.

I want to split one super-project with multiple branches into multiple projects with one main branch:

super-project (branch-a, branch-b) -> project-a (main) + project-b (main), where branch-a at super-project == main at project-a and branch-b at super-project == main at project-b

I have a single Gerrit instance with NoteDb backend. I want to save the whole change history with the same change numbers but altered branches and projects. Changes must not be duplicated.

The solution I see is:

1. Stop Gerrit,
2. Initialize a new project-a.git bare repo in Gerrit's git directory,
3. Push refs/meta/config at super-project to refs/meta/config at project-a as is,
4. Push refs/heads/branch-a at super-project to refs/heads/branch-a at project-a as is,
5. Find refs/changes/<change-number>/meta which nearest parents have "Branch: branch-a" trailer and push refs/changes/<change-number>/* from super-project to project-a as is,
6. Rename branch-a to main,
7. Commit "Branch: main" trailer to the pushed refs/changes/*/meta references,
8. Do the same for project-b,
9. Delete super-project,
10. Rebuild cache and index.

Am I right that this method will do what I want?

Cheers,
Daniil Gankov

[Sven Selberg]

On Tuesday, June 17, 2025 at 5:29:43 PM UTC+2 Daniil Gan’kov wrote:

Hello.

I want to split one super-project with multiple branches into multiple projects with one main branch:

super-project (branch-a, branch-b) -> project-a (main) + project-b (main), where branch-a at super-project == main at project-a and branch-b at super-project == main at project-b

I have a single Gerrit instance with NoteDb backend. I want to save the whole change history with the same change numbers but altered branches and projects. Changes must not be duplicated.

The solution I see is:

1. Stop Gerrit,
2. Initialize a new project-a.git bare repo in Gerrit's git directory,
3. Push refs/meta/config at super-project to refs/meta/config at project-a as is,
4. Push refs/heads/branch-a at super-project to refs/heads/branch-a at project-a as is,

If the branch will be called main eventually I don't think you have anything to gain by pushing to branch-a and renaming it, I'd push the branch directly to project-a:refs/heads/main.

[Nasser Grainawi]

It looks like it could work. Please do share back here with your results as I haven't seen someone attempt this scenario previously :)

 

Cheers,
Daniil Gankov

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[Daniil Gan’kov]

It seems to work.

But there are some remarks on the implementation:

1. It is not easy to just share refs/meta/config between projects especially when branches are renamed. I found it is simpler to configure the moved project from scratch.
2. "Branch: <new>" trailer is not enough for the commit over refs/changes/*/meta. It also must contain "Patch-set: <latest>" for Gerrit to reindex changes without an exception.
3. refs/notes/review becomes inconsistent after these actions. As I found, it is enough to just run "reviewnotes export" over SSH to update these refs over all projects.

And thanks, Sven, for your advice.