The Changelog

As of today, hg.complete.org is no more. I have removed mercurial and hgwebdir from my server, removed hg from my DNS zone, and converted everything that was in Mercurial over to Git. (Except for hg-buildpackage, which I have orphaned) So there is now stuff at git.complete.org.

I still have a ton of Darcs repos to convert, which will take more time.

Also I have heard a lot of people say that the GitPlugin for Trac is not very good. I have two Trac instances running it: one for commithooks and another for ListLike. Both seem OK so far, but I haven't pushed them very much yet.

Exactly one year ago today, I wrote about Git, Mercurial, and Bzr. I have long been interested in VCS, and looked at the three main DVCS systems back then.

A Quick Review

Mercurial was, and for the moment, remains, my main VCS. Bzr remains really uninteresting; I don't see it offering anything compelling that Mercurial or Git can't do. My Git gripes mainly revolved around its interface and documentation. Also, I do have Windows people using my software, and need a plausible solution for them, even though I personally do no development on that platform.

Ted Tso wrote his own article in reply to mine, noting that the Git community had identified many of the same things I had ans was working on them.

I followed up to Ted with:

... So if Ted's right, and a year from now git is easier to use, better documented, more featureful, and runs well on Windows, it won't be that hard to switch over and preserve history. Ted's the sort of person that usually is right, so maybe I should starting looking at hg2git right now.

So I guess that means it's time to start looking at Git again.

This is rather rambly, I know. It's late and I want to get these thoughts down before going to sleep...

Looking at Git

I started at the Git wikipedia page for an overview of the software. It linked to two Google Tech Talks about Git: one by Linus Torvalds and another by Randal Schwartz. Of the two, I found Linus' more entertaining and Randal's more informative. Linus' point that CVS is fundamentally broken, and that SVN trying to be "a better CVS" (an early goal of svn, at least) means it too is fundamentally broken, strikes me as quite sound.

One other interesting tidbit I picked up is that git can show you where functions have moved from one file to another, thanks to its rename-detection heuristic. That sounds really sweet, and is the best reason I've yet heard for Git's stubborn refusal to track renames.

The Landscape

I've been following Mercurial and Darcs somewhat, and not paying much attention to Git. Mercurial has been adding small features, and is nearing version 1.0. Darcs has completed a major overhaul both of its repository format and internal algorithms and is nearing version 2.0, and appears to have finally killed the doppleganger (aka conflict spinlock) bug for good.

Git, meanwhile, seems to have made strides in usability and documentation in its 1.5.x versions.

One thing particularly interesting to me is: what projects are using the different VCSs. High-profile projects now using Mercurial include OpenSolaris, OpenJDK (Java 7), and Mozilla's projects. Git has, of course, the Linux kernel. It also has just about everything associated with freedesktop.org, including X. Also a ton of Unixy stuff.

Both Mercurial and Git communities are working on TortoiseHg/TortoiseGit types of GUIs for Windows users. Git appears to have a sane Windows port now as well, putting it on pretty much even footing with Mercurial and Darcs there. However, I didn't spot anything with obvious Windows ties in the Git "what projects use git" pages.

The greater speed of Mercurial and Git -- even for pushing and pulling small patches -- likely will keep me away from Darcs for the moment.

Onwards...

As time allows (I do have other things keeping me busy), I plan to install git and work through some tutorials and try to use it in practice as much as possible, to get a good feel for it.

Future

It is beneficial to be using a VCS that is popular, though that is certainly not a major criterion for me. I refuse to use SVN because its lack of distributed functionality makes it too unproductive to be useful. But it looks like Git is gaining a lot of traction these days, especially in Debian circles, which also makes it more interesting.

I notice that Ted did convert e2fsprogs over to git as he said he might, incidentally.

I've talked a lot lately about different VCSs.

I got some interesting comments in reply to my most recent post. One person took issue with my complaint that nobody really understood how to specify a revision to git format-patch, and proceeded to issue an incorrect suggestion. And a couple of people complained about my comments about bzr, which generally came down to the released version of bzr didn't have anything compelling and also didn't support tags.

So I went into #bzr, asked them what bzr has that git, Mercurial, and darcs don't. And gave bzr the benefit of the doubt that 0.15 will be out soon and will be stable. What I got back were these general items:

1. Renaming of directories (not in hg, git)
2. 2-way sync with Subversion (not in hg, darcs)
3. Checkouts (not in any others by default)
4. No server-side push requirement

Let's look at these in more detail.

1. Renaming of directories

All of them can rename files and (excepting git) completely accurately track back the file's history. But consider this: if person A commits a change to branch A that adds a file, and person B then renames the directory that the file is in on his branch, will a merge cause person A's file to appear in the new directory name? In darcs and bzr, yes. In Mercurial and git, no.

So yes, this is a nice thing. But I have never actually had this situation crop up in practice, and even if it did, could be trivially remedied. I would say that for me, I don't really care.

[Update: Current stable releases of Mercurial can do this too. I'm not quite sure how, but it does work. So git is the only one that can't do that.]

2. 2-way sync with Subversion

This is a really nice feature and is present in both git and bzr. I haven't tested it either place, but if it works as advertised -- and properly supports tracking multiple related svn branches and merges -- would be slick. That was enough to make me consider using git, but in retrospect, I so rarely interact with people using svn that it is not that big a deal to me.

Still, for those that have to work with svn users, this feature in bzr and git could be a big one.

Better yet would be to get all those svn holdouts over to DVCS.

3. Checkouts

A bzr checkout is basically a way to make local commits be pushed to the remote repo immediately, as with svn. This is of no utility to me, though I can see some may have a use for it. But it can be done with hg hooks and probably approximated with scripting in others.

4. No server-side process necessary for pushing repos

bzr has built-in support to push to a server that has sftp only, and doesn't require a copy of itself on the server. While I believe that none of the other three have that, it is possible to rsync (and probably ftp) darcs and Mercurial repos to a server in a safe fashion by moving repo files in a defined order. Probably also possible with git. All four can pull repos using nothing but regular HTTP.

What bzr still doesn't have

Integrated patch emailing. The big thing is that it has no built-in emailing of patches support. darcs is extremely strong in this area, followed by hg, and git is probably third. "darcs send" is all it takes to have darcs look at the remote repo, figure out what you have that they don't, and e-mail a bundle of changesets to them. I posted an extension and later a patchset that does all this for Mercurial except for automatically figuring out what default email address to do (that'll come in a few days, I think). One feature Mercurial has had for awhile that Darcs hasn't is sending multiple textual diffs as a thread, with one message per changeset. bzr doesn't have any support for emailing patches yet, which is disappointing. Because of the strong support for this in darcs and Mercurial, people running those systems feel less of a need to publish their repos.

[Update: There is a plugin for bzr that seems to address some of this. I haven't tested it, and it's not in bzr core (so doesn't quite meet my very friendly for a newbie requirement), but this does exist, though apparently not as advanced as Mercurial]

Performance. Supposedly 0.15 is supposed to be better on this, but even if bzr achieves the claimed doubling of performance, most benchmarks I have seen would rate it as still being significantly behind git and Mercurial, though it may overtake darcs in some tests.

Extensive documentation. I would say that bzr's docs are better in some ways than git's (its tutorials especially), but lack depth. If you want to know some detail about how the repository works on-disk, it's not really documented. Darcs still has David's excellent manual, and Mercurial has the hg book which is still great as well.

Merging not as advanced. darcs is pretty obviously way on top here, but of the others, Mercurial does a pretty good job with its automatic handling of renames and automatic resolving of different branches that commit the same change (even if that same change is a rename, or an add of the same content). bzr can't resolve as much automatically.

Summary

Well, I'll say that bzr still doesn't look compelling enough for my use cases to use, and the lack of an easy-for-a-newbie-to-use automated email submission feature is a pretty big disappointment. Though I did appreciate the time those on #bzr spent with me, and if I needed to sync with svn users frequently, I'd probably choose bzr over git.

For now, I'm happy with sticking with darcs for my code and hg for my Debian work.

But all four communities are aggressively working on their weaknesses, and this landscape may look very different in a year.

I've been writing a lot about this lately, I know, but it's an interesting landscape.

I had previously discarded git, but in light of git-cvsserver (which provides a plausible way for Windows people to participate), I gave it a try.

The first thing I noticed is that git documentation, in general, is really poor. Some tutorials that claim to cover git actually cover cogito. Still others use commands that are much more complex than those in the current git -- and these just the ones linked to from the git homepage.

git's manpages aren't much better. There are quite a few git commands (such as log) that take arguments that other git commands accept. Sometimes this fact is documented with a pointer to these other commands, but often not; a person is left guessing what the full range of accepted arguments are.

My complaint that git is overly complex still exists. They've made progress, but still have a serious issue here. Part is because of the docuemtnation, and part is because of the interface. I wanted to export to diffs all patches on the current branch in a repo. I asked on #git, and someone suggested using the revision specifier ..HEAD. Nope, didn't work. A few other git experts chimed in, and none could come up with the correct recipe. I finally used -500, which worked but is hackish.

git's lack of even offering support for a human to indicate renames also bothers me, though trustworthy people have assured me that it doesn't generally cause a problem in practice.

git does have nicer intra-repo branching than Mercurial does, for the moment. But the Mercurial folks are working on that anyway, and branching to new directories still works fine for me.

But in general, git's philosophy is to make things easy for the upstream maintainer, and doesn't spend much effort making things easy for contributors (except to make it mildly easier to contribute to a large project like Linux). Most of my software doesn't have a large developer community, and I want to make it as easy as possible for new developers to join in and participate. git still utterly fails on that.

I tried bzr again. It seems that every time I try it, after just a few minutes, I am repulsed. This time, I stopped when I realized that bzr doesn't support tags and has no support for emailing changesets whatsoever. As someone that has really liked darcs send (and even used tags way back with CVS!), this is alarming. The tutorial on the bzr website referenced a command "bzr help topics", which does not work.

So I'll stick with my mercurial and darcs combination for now.

I announced the first version of a hg send extension yesterday as well. I think Mercurial is very close to having a working equivalent to darcs send.

About two weeks ago, I wrote about my thoughts on Mercurial and how I was switching to it from Darcs.

At the time, I had skipped Git because of its lack of Windows support. I have some contributors to pieces of Free Software that I write that use Windows, and that seemed a pretty big flaw.

But I recently discovered git-svn and git-svnimport, both of which look like great tools for working with our friends using svn that haven't yet gotten ahold of the DVCS light. Then I noticed that Git has a CVS server emulation tool, which means that Windows users can use TortoiseCVS to interact with it. Nice.

I spent some time today learning Git. This was a lot easier having already learned Mercurial. Git and Mercurial have very similar philosophies to a number of things, but the Mercurial documentation explains all this far better than the Git documentation does.

I'm going to have to try both of them out more and see what I think. But git-svn (which is bi-directional) certainly looks like a very nice thing.

Neither of them have something as nice as darcs send, though.

I have been tracking 2.6.16.x here because Xen doesn't have patches for 2.6.17 yet (why on earth that is, I don't know.) But I need a few 2.6.17.x patches to the qla2xx driver. So I figure this is an opportunity to learn git.

I learned git, but then quickly learned that I can't just pull random commits from one branch to another. I have to use git cherry-pick, which doesn't actually pull the commit unmodified -- it takes a diff, and commits a new patch based on that diff. So I expect problems later when I bump the local branch to 2.6.17.

This seems depressingly like arch/baz/bzr, and is a good reason for me to stay with darcs for now. This same operation with darcs would have been trivial, AND darcs would have automatically pulled in prerequisite patches rather than giving a merge failure and making me find them manually.