On Tue, Apr 01, 2014 at 07:45:03AM -0400, Jeff King wrote: > On Tue, Apr 01, 2014 at 07:25:54PM +0900, Mike Hommey wrote: > > > I am currently prototyping a "native" mercurial remote handler for git, > > For my own curiosity, how does this differ from what is in > contrib/remote-helpers/git-remote-hg?
contrib/remote-helpers/git-remote-hg does a local mercurial clone before doing the git conversion. While this is not really a problem for most mercurial projects, it tends to be slow with big ones, like the firefox source code. What I'm aiming at is something that can talk directly to a remote mercurial server. > > Would adding a fast-import command to handle deltas be considered useful > > for git? If so, what kind of format would be suitable? > > It breaks fast-import's "lowest common denominator" data model that is > just passing commits and their contents over the stream. But we already > do that in other cases for the sake of performance. I think the > important thing is that the alternate formats are optional and enabled > by the caller with command-line options. > > That being said, I foresee a few complications: > > 1. Git needs to know the sha1 of the full object. So unless the > generating script knows that ahead of time, git has to expand the > delta immediately anyway (this could still be a win if we end up > using a good delta from elsewhere rather than doing our own delta > search, but I suspect it's not so big a win as if we can just blit > the delta straight to disk). Good point. That could quickly become a problem with long delta chains. > 2. Git does not store on-disk deltas between objects that are not in > the same packfile. So you'd only be able to delta against an object > that came in the same stream (or you'd have to "fix" the packfile > on disk by adding an extra copy of the delta base, but that > probably eliminates any savings). Arguably, this would make the most difference on initial clone of big projects, or large incremental updates (like, after a few weeks), which would use a single pack anyways. > As for format, I believe that git is basically xdelta under the hood, so > you'd want either that or something that can be trivially converted to > it. It seems to me fast-import keeps a kind of human readable format for its protocol, i wonder if xdelta format would fit the bill. That being said, I also wonder if i shouldn't just try to write a pack on my own... Cheers, Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
