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Re: [jgit-dev] Ketch: multi-master replicated Git

Hi Shawn,
worth sharing on the repo-discuss mailing list as well :-)

Could then I use Git Ketch to manage the agreement process on pushes (as Cassandra gives me some headache with that) and still use another DFS implementation based on Git objects on Cassandra?


> On 13 Jan 2016, at 14:54, Shawn Pearce <spearce@xxxxxxxxxxx> wrote:
> Google is starting to contribute a new multi-master implementation,
> calling it Git Ketch. Changes are on the Eclipse Gerrit[1].
> What is Git Ketch?
> ------------------
> Git Ketch is a multi-master Git repository management system. Writes
> (such as git push) can be started on any server, at any time. Writes
> are successful only if a majority of participant servers agree.
> Acked writes are durable against server failure, due to a majority of
> the participants storing all required objects.
> Do I need DFS?
> --------------
> No. We realized not everyone wants to run JGit DFS. Git Ketch is a
> higher-level, storage-agnostic service that can use both classical
> local file repositories, and DFS type repositories.
> Do I need JGit?
> ---------------
> Sort of.
> The Ketch Leader process running the consensus algorithm is currently
> implemented in Java, relying on JGit. However...
> Any Git repository served by Git >= 2.4.0 can act as a voting
> participant (the required feature is `git push --atomic`). The
> consensus algorithm runs on the Git wire protocol.
> Where's the rest?
> -----------------
> Google's prior multi-master implementation is 4 years old and heavily
> intertwined with internal source code. We are rewriting the
> multi-master logic and open sourcing as we go. We think this will make
> it easier for the JGit project to review and digest.
> Unfortunately, major portions are being rewritten from scratch, as
> there are segments deeply connected to our internal implementation of
> JGit DFS on Google Bigtable, or to our internal authentication and RPC
> protocols. None of that makes sense in the open source JGit project.
> So, the rest is Coming Soon(TM). We are working on it.
> You can help by providing feedback. :)
> Why is it called Git Ketch?
> ---------------------------
> Git Ketch is modeled on the Raft Consensus Algorithm[2]. A ketch[3]
> sailing vessel is faster and more nimble than a raft[4]. It can also
> carry more source codes.
> Git Ketch front-loads replication costs, which we think vaguely
> resembles a ketch sailing vessel's distinguishing feature of the main
> mast on the front of the ship.
> Footnotes
> ---------
> [1]
> [2]
> [3]
> [4]
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