VCS comparison table
torvalds at osdl.org
Sat Oct 21 22:04:56 BST 2006
On Sat, 21 Oct 2006, Erik Bågfors wrote:
> bzr is a fully decentralized VCS. I've read this thread for quite some
> time now and I really cannot understand why people come to this
Even the bzr people agree, so what's not to understand?
The revision numbers are totally unstable in a distributed environment
_unless_ you use a certain work-flow. And that work-flow is definitely not
"distributed" it's much closer to "disconnected centralized".
Now, you could be truly distributed: BK used the same revision numbering
thing, but was distributed. But BK didn't even try to claim that their
revision numbers were "simple" and that fast-forwarding is sometimes the
wrong thing to do.
So BK always fast-forwarded, and the revision numbers were just randomly
changing numbers. They weren't stable, they weren't simple, and nobody
claimed they were.
So bzr can bite the bullet and say: "revision numbers are changing and
meaningless, and we should just fast-forward on merges", or you should
just admit that bzr is really more about "disconnected operation" than
You can't have your cake and eat it too. Truly distributed _cannot_ be
done with a stable dotted numbering scheme (unless the "dotted numbering
scheme" is just a way to show a hash like git does - so the numbering has
no _sequential_ meaning).
Btw, this isn't just an "opinion". This is a _fact_. It's something they
teach in any good introductory course to distributed algorithms. Usually
it's talked about in the context of "global clock".
Anybody who thinks that there exists a globally ticking clock in the
system (and stably increasing dotted numbers are just one such thing) is
talking about some fantasy-world that doesn't exist, or a world that has
nothing to do with "distributed".
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