Re: VCS comparison table

From: David Clymer <david@zettazebra.com>
Date: Oct 24, 2006, 03:24 UTC
Message-ID: <1161660291.22276.209.camel@zepto.home.zettazebra.com>
In-Reply-To: <200610231454.06355.jnareb@gmail.com>

On Mon, 2006-10-23 at 14:54 +0200, Jakub Narebski wrote:

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> On Mon, Oct 23, 2006 David Clymer wrote:
> > On Sun, 2006-10-22 at 22:06 +0200, Jakub Narebski wrote:
> >> David Clymer wrote:
> 
> >>> 2. bzr does not support fully distributed development because revnos
> >>> "don't work" as stated in #1.
> >>
> >> Bazaar is biased towards centralized/star-topology development if we
> >> want to use revnos. In fully distributed configuration there is no
> >> "simple namespace".
> > 
> > So revnos aren't globally meaningful in fully distributed settings. So
> > what? I don't see how this translates into bias. There is a lot of
> > functionality provided by bazaar that doesn't really apply to my use
> > case, but it doesn't mean that it is indicative of some bias in bazaar.
> 
> First, bzr is biased towards using revnos: bzr commands uses revnos
> by default to provide revision (you have to use revid: prefix/operator
> to use revision identifiers), bzr commands outputs revids only when
> requested, examples of usage uses revision numbers.

Agreed. Of course, I want the simplest case to be the simplest. When working on my own branch, regardless if it is a standalone project or part of a distributed one, I don't want to have to type SHA hashes or revids. Numbers serve my purposes best in this case. When I communicate with other distributed developers, I can and should use revids.

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> 
> In order to use revnos as _global_ identifiers in distributed development,
> you need central "branch", mainline, to provide those revnos. You have
> either to have access to this "revno server" and refer to revisions by
> "revno server" URL and revision number, or designate one branch as holding
> revision numbers ("revno server") and preserve revnos on "revno server"
> by using bzr "merge", while copying revnos when fetching by using bzr "pull"
> for leaf branches. In short: for revnos to be global identifiers you need
> star-topology.

Ok. Let's not repeat this again. I think I said this once, and you've said it in two following emails. It's a given. Assume that we all know it.

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> 
> Even if you use revnos only locally, you need to know which revisions are
> "yours", i.e. beside branch as DAG of history of given revision you need
> "ordered series of revisions" (to quote Bazaar-NG wiki Glossary), or path
> through this diagram from given revision to one of the roots (initial,
> parentless revisions). Because bzr does that by preserving mentioned path
> as first-parent path (treating first parent specially), i.e. storing local
> information in a DAG (which is shared), to preserve revnos you need to
> use "merge" instead of "pull", which means that you get empty-merge in
> clearly fast-forward case. This means "local changes bias", which some
> might take as not being fully distributed.

"local changes bias" I can buy that. I even like it. I don't even care if that makes bazaar "not fully distributed." I don't think the distinction between "fully" and "almost, except for some technicality" distributed is one that has much practical value.

-davidc

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