josh VS git-repo

Why use submodules when you can properly vendor the upstream git, and export/import commits without breaking hashes on either side?

https://github.com/josh-project/josh

We've been using josh at TVL for years and it's just amazing.

Scalar explicitly does not implement the virtualized filesystem the OP is referring to. The original Git VFS for Windows that Microsoft designed did in fact do this, but as your second link notes, Microsoft abandoned that in favor of Scalar's totally different design which explicitly was about scaling repositories without filesystem virtualization.

There's a bunch of related features they added to Git to achieve scalability without virtualization. Those are all useful and Scalar is a welcome addition. But the need for a virtual filesystem layer for large-scale repositories is still a very real one. There are also some limitations that aren't ideal; for example Git's partial clones IIRC can only be used as a "cone" applied to the original filesystem hierarchy. More generalized designs would allow mapping any arbitrary paths in the original repository to any other path in the virtual checkout. Tools like Josh can do this today with existing Git repositories[1]. That helps you get even sparser and smaller checkouts.

The Git for Windows that was referenced isn't even that big at 300GB, by the way. Game studios regularly have repositories that exist at multi-terabyte size, and they have also converged on similar virtualization solutions. For example, Destiny 2 uses a "virtual file synchronization" layer called VirtualSync[2] that reduced the working size of their checkouts by over 98%, multiple terabytes of savings per person. And in a twist of fate, VirtualSync was implemented thanks to a feature called "ProjFS" that Microsoft added to Windows... which was motivated originally by the Git VFS for Windows they abandoned!

[1] https://github.com/josh-project/josh

[2] https://www.gdcvault.com/play/1027699/Virtual-Sync-Terabytes...

Good overview, I know these sorts of pains well. Lots of hard questions and few definitive wins/right answers. How to organize a massive repository out in the open is still an open question. On that note, recently, I've been experimenting with this project called josh, which basically is like 'git subtree on extreme steroids, functioning as a git proxy':

https://josh-project.github.io/josh/

It basically lets you unify/view many repositories as a single one, or equivalent to split a mono-repo into smaller sized units of work for CI, specific teams, etc. It's bidirectional, so you push and pull from josh and everything goes into a single linear history in the mono repo. And because it's bidirectional, people in the mono-repo can still do things like make large-scale atomic changes across all sub-repositories, and those get reflected.

Josh currently isn't suitable for a lot of workloads due to various reasons (authentication is one that stands out), but it's actually the first tool I have seen that manages to offer BitKeeper-like "subtrees" that work really well, at scale, for large repos and teams. It requires some care to make sure "sub-trees" can be usable units of work, but it was one of the best features of BK in my opinion and really great for people doing one-off contributions, or isolating trees/changes to specific developers.

I'd be interested to know if there are other open alternatives to this. It's a nice point in the design space between solutions like "integrate with the filesystem layer to do sparse clones" or "just split up the repos."

With regard to repo composition, I have been following this project: https://github.com/josh-project/josh

There is another option - “repo” - which is basically souped-up submodules but requires a third-party tool. It might make sense depending on your use case though. It’s pretty powerful.

I assume the parent comment refers to this, to save others googling "git repo"..

https://github.com/GerritCodeReview/git-repo