On Thu, Feb 04, 2016 at 03:17:59AM -0500, Jeff King wrote: > On Thu, Feb 04, 2016 at 05:12:20PM +0900, Mike Hommey wrote: > > > > > It seems like git branch -d ascend the hierarchy (up to > > > > .git/refs/heads/), deleting any empty directories. > > > > > > Yes, though it needs to be coupled with making the branch-creation > > > process more robust to races (since we might create "refs/heads/foo" in > > > order to make "refs/heads/foo/bar" while somebody else is deleting it to > > > get rid of "refs/heads/foo/baz"). > > > > Can't we come up with a system that would update packed-refs directly > > instead of creating files? > > There are a few reasons not to: > > - it breaks backwards compatibility (unless we continue to create the > directory in order to put the dot-lock in it, but then I don't think > we've gained anything) Is that the kind of backwards compatibility that matters, though? I mean, I won't claim to know all the internals of how refs are used, but you sound like the theoretical incompatibility would be two different versions of git racing for update-ref on the same local repository. Not that it would change anything about the other reasons below. > - the usual update method for packed-refs is to take a dot-lock, do a > whole-file update, and then atomically rename into place. That > makes writing a ref O(# of refs) instead of O(1), and increases lock > contention on the packed-refs file. > > - if we abandon atomic renames as the update mechanism and just update > in place via lseek/write, then we need read-locking, or we need to > hope that a reader will never see a sheared write > > But if we're willing to break compatibility, we should ditch packed-refs > entirely and move to a _real_ concurrent database. And there is work > underway already to do that (see David Turner's ref-backend-lmdb > series). Mike -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html