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Re: [rdiff-backup-users] Restarting development

From: Josh Nisly
Subject: Re: [rdiff-backup-users] Restarting development
Date: Tue, 06 Apr 2010 09:27:58 -0500
User-agent: Thunderbird (X11/20100317)

Daniel Miller wrote:
Hi Josh,

Development on rdiff-backup has stagnated for the last while. I think that this is attributable to several reasons:
* Andrew has dropped of the face of the earth, (he's working on graduate studies, IIRC) and I've been busy with other things. Since we're the two core maintainers, that tends to slow things down.
* I started work on unicode support, but realized that it requires a transition period. In current CVS, it's broken just enough to make life difficult.
* The code isn't structured all that well. This is at least partially because we don't have good automated tests, so it's hard to refactor without breaking things.
* We're still using CVS :-)

Thanks for bringing up these issues to get development started again. I didn't intend to hijack your thread...

I'm interested in collaborating with you going forward if you're interested in the same. I will attempt to migrate my git repo to hg if that's what you want, although I haven't used hg before, so it will be new for me. I am reluctant to publish the code under the rdiff-backup name if you are not interested in working on the new codebase. How would you like me to handle that? Would you like a copy of the code so you can have a look over it before you make any decisions? It's still pretty new, and there is definitely more work to do to implement the features I have planned and to bring it up to par on all of the currently supported platforms.

A little background on why I went down this road: you may remember my posts back in Feb on the full-verify patch. I had a working patch that I had contributed and started using on my system. I was very careful when I developed that patch because I wanted it to be useful on a production system. Then, the first time I tried to start a new repository with that patch applied I got all kinds of strange errors. This really made me worried because I had no idea why it happened--the errors just didn't make any sense. Since then, I tried again with the same setup, and it worked the second time! That's even more frightening... to me it says there is something non-deterministic in the design of rdiff-backup (it could be something in my setup too, although I've gone over it and even run it by others many times). Since then I've been using a version of rdiff-backup 1.2.8 with my full-verify patch (and some minor tweaks), and its been working well. Surprisingly, and somewhat unbelievably, the new verify mechanism detected a hard drive going bad on my system, so I'm glad I'm using it. Soon after the verify started failing I had other warnings as well (rsync started failing too) so it's not like I wouldn't have known if I didn't have the full-verify, but it gave me the earliest warning.

After that experience I decided that I would try a redesign to see how far I could get. If it never goes anywhere, no problem, it has been fun to solve the problems and learn how the rsync algorithm works and is used in rdiff-backup. But I think this new design is much cleaner, and opens up a lot of potential for long-awaited features to be added to rdiff-backup. I'm be interested to hear your thoughts.
First, I'm delighted that you're taking an interested in the project! More creativity (and competition) is a good thing.

Here's my personal perspective. Our current users get grumpy when we change the wire protocol across major versions - I suspect that losing backwards compatibility at the repository level would be a deal-killer for many. (I know it would be for me, since I have hundreds of repositories with multiple years of history.) Because of that, I doubt that I'll contribute meaningfully to a new project. I'm also a little hesitant to call it rdiff-backup, since it is a complete rewrite. Maybe rdiff-backup-ng (or something like that) would be a good compromise?

I'm a little torn - I don't want to discourage you from starting from scratch at all, but I think that the current codebase has lots of value in it that make it worth salvaging. I can understand where you're coming from to start a new version, yet I wonder if you might not be underestimating the amount of work required to bring it to parity with the current codebase. Supporting OS X resource forks and Windows ACLs, for example. A lot of value that I see in rdiff-backup is in its myriad of workarounds for handling all sorts of situations, from simple things like chmod'ing unreadable files temporarily to be able to back them up, to handling backups from a unix (case-sensitive) file system to a windows (case-insensitive) one.

Personally, I'd like to have your help developing tests for the current codebase. I really think that if we come up with good functionality tests, we can refactor the codebase to the point where we can start writing unit tests. However, that's certainly less enjoyable than starting from scratch(!), so I can't blame you for not getting excited about that.

I'm looking forwarding to hearing your responses.

Thanks for your interest and input so far!


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