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Re: major Subversion progress

From: Karl Fogel <kfogel_at_collab.net>
Date: 2001-07-13 17:44:06 CEST

Timothee Besset <timo@qeradiant.com> writes:
> I'm waiting for the first "usable" version with a cvs2svn repository
> to start playing with it. But actually, is it planned to have some
> svn2cvs feature? I can conceive that it has not a lot of interest for
> you guys, but since there won't be a lot of SVN clients in the first
> versions (specially graphical ones), I don't think I would be able to
> get all my developers to make the switch..

Well, your conjecture is right -- at least, I can't see how it would
be a good use of any Subversion developer's time to work on
svn2cvs. :-)

Of course svn2cvs would be useful for some people; I guess either a
volunteer will need to step forward, or (perhaps) it will be important
enough to some organization that they will fund its development.

I'm talking about a repository conversion program, by the way, not a
cvs client that is able to talk to Subversion repositories. Both are
possible, but the latter is probably harder than the former. Either
one would have to lose information (directory versions, properties),
since Subversion versions a proper superset of what CVS versions.


> On Thu, 12 Jul 2001 17:38:44 -0500
> Karl Fogel <kfogel@collab.net> wrote:
> > I know not everyone is following the CVS commit mails closely, so I'd
> > like to point out that something totally awesome just happened:
> >
> > The Subversion repository now does deltified storage. In other words,
> > we can take our filesystem code seriously now! :-) Big-time kudos to
> > Mike Pilato <cmpilato@collab.net> for finishing this one off.
> >
> > This was the last truly major coding task on the todo list, as far as
> > Subversion itself goes -- everything else we need to get to alpha is
> > relatively small: keyword substitution and newline conversion, some
> > fixes in the working copy code, etc. Some things, like the hook and
> > auth systems, need some more design think-time, but once designed,
> > they are easy to implement.
> >
> > A couple of notes:
> >
> > 1. There is still one big thing that needs to happen before M3: a
> > cvs2svn repository converter :-). If anyone wants to volunteer,
> > that would be a fine thing... You wouldn't be all alone: many
> > on this list have a good understanding of how the converter
> > needs to work, and various ways to make it efficient. The main
> > reason this is a big task is that the converter needs to have a
> > *very* thorough test suite, because (obviously) we can't afford
> > to corrupt data.
> >
> > 2. The deltification code still has room for improvement. While
> > the conversion from fulltext to delta is quite efficient
> > (probably only minor improvements are possible from here), the
> > undeltification code will probably want tweaking at some point
> > in the future. Currently, fulltext reconstruction uses memory
> > proportional to the delta window size times the number of
> > intermediate deltas between the target and the "base" fulltext
> > (the latter usually being the most recent revision of the
> > object); there are also some running time issues.
> >
> > Regarding (2):
> >
> > Mike, Ben, and I all feel is that it would be premature optimization
> > to write the Ultimate Efficient Delta Combiner at this time, when
> > there are so many other important tasks that need doing. It is
> > perfectly acceptable to get to 1.0 with the undeltification method we
> > have now, which should perform well enough in most circumstances.
> >
> > Doing real delta combination will get us a big-O improvement for
> > retrieving large files, and we more or less know how to do it.
> > However, it is a very complex coding task and IOHO it's more important
> > to get Subversion to feature-completeness than to optimize every last
> > drop out of the delta reconstruction algorithm. (This is not intended
> > to discourage others from working on it right now if they want, of
> > course!)
> >
> > With all this in mind:
> >
> > Mike and I are going to spend tomorrow writing a slew of new fs tests,
> > whose goal will be to stress the new deltified storage code, and make
> > sure it performs acceptably at least where CVS performs acceptably.
> > Then starting Monday, we're going to bid the deltification code adieu
> > and join everyone else on the rest of alpha-checklist.txt. The goal
> > is to get foolproof regression insurance in place and then move on.
> > That way, when we later do improve the algorithm, we will know right
> > away if it works and won't need to worry about whether it's
> > functionally equivalent to the old code.
> >
> > Okay, enough happy-talk, clearly there's still a lot of code to write.
> > Back to work now... Keep those patches coming!
> >
> > -K
> >
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Received on Sat Oct 21 14:36:33 2006

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