Re: Lockless Refs?

[Jeff King <peff@peff.net>]

On Fri, Dec 28, 2012 at 09:15:52AM -0800, Junio C Hamano wrote:

> Martin Fick <mfick@codeaurora.org> writes:
> 
> > Hmm, actually I believe that with a small modification to the 
> > semantics described here it would be possible to make multi 
> > repo/branch commits work....
> >
> > Shawn talked about adding multi repo/branch transaction 
> > semantics to jgit, this might be something that git wants to 
> > support also at some point?
> 
> Shawn may have talked about it and you may have listened to it, but
> others wouldn't have any idea what kind of "multi repo/branch
> transaction" you are talking about.  Is it about "I want to push
> this ref to that repo and push this other ref to that other repo",
> in what situation will it be used/useful, what are the failure
> modes, what are failure tolerances by the expected use cases, ...?
> 
> Care to explain?

I cannot speak for Martin, but I am assuming the point is to atomically
update 2 (or more) refs on the same repo. That is, if I have a branch
"refs/heads/foo" and a ref pointing to meta-information (say, notes
about commits in foo, in "refs/notes/meta/foo"), I would want to "git
push" them, and only update them if _both_ will succeed, and otherwise
fail and update nothing.

I think Shawn mentioned this at the last GitTogether as a stumbling
block for pushing more of Gerrit's meta-information as refs over the git
protocol. But I might be mis-remembering.

-Peff