gitolite/contrib/gerrit.mkd

comparing gerrit and gitolite

Gerrit and gitolite have too many high level differences. Size is most visible of course: 56000 lines of Java versus 1300 lines of perl+shell, according to David A. Wheeler's 'SLOCCount' tool. Gerrit needs a database (it comes with a perfectly usable one, or I believe you can use any of the usual suspects), and even comes with its own ssh server and git server, and since the git engine is internal it probably has to include a lot of things that normal git already has; I wouldn't know for sure.

Gerrit allows a lot more de-centralisation in managing the system, and of course excels at code review, and it seems geared to really large, open source-ish projects with lots of contributors.

Gitolite works on a pure command-line install and a plain text file config, and is designed to run unobtrusively and quite transparently to all developers -- other than sending the admin their pubkey, nothing really changes for them in their workflow, toolset, etc. The "lite" in the name still holds, despite all the extra features being pumped in!

Gitolite was mainly written for a corporate environment, where we really, really, need branch-level ACLs. While they would certainly love the code review part, things like voting on a change, and so on seem a bit alien, and it seems to me that code review itself is more likely to be a hierarchical thing, not a peer-to-peer, "anyone can comment" thing. I could be wrong.

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In short, gitolite doesn't do the main thing that gerrit does, and gerrit is so much bigger than gitolite in so many ways, it seems really odd to compare them at all.

However, it seems gerrit comes closest to gitolite in terms of flexibility of access control, which is gitolite's main strength, so I thought it would be useful to compare gitolite with just what is in the "access-control.html" in the gerrit war file. Or see this. [...and stop sniggering at the "svn" in the link dammit!]

Note that I don't necessarily list something that both tools have. (For example, per-user branches denoted by /USER/ in gitolite and $(username) in gerrit, or being able to distinguish between creating a branch and pushing to an already created one, etc).

Administrators: anyone who has gitolite-admin push privs

Anonymous Users: gitolite doesn't do that, though the "ssh-plus" branch, combined with git-daemon2 (Ilari) will allow that in future. When git-daemon2 becomes mainstream, the supporting code in this branch will also be merged into "master".

Registered Users: @all

Account Groups: @groups in gitolite. We do allow them to be nested, although the parsing is single-pass. We also don't have group foo-admin managing membership to group foo though; all groups are managed by the eqvt of "Administrators".

Project ACLs: first, let's remember (again) that we don't have any of the code review stuff :)

• This is a subjective point, but gerrit doesn't give permissions to individual users, only groups. People who have several small projects (only one QA, one integrator, etc.), would have to create lots of 1-man groups, which could be cumbersome.

• Evaluation order and priority of access control rules are different. Gerrit goes by specificity, gitolite goes by sequence. It shouldn't matter; they're probably equivalent except perhaps in some far-fetched scenarios.

• One big difference is that gitolite does not process "deny" rules ("-1 no Access" in gerrit terms) for read access -- we only support those for write access. Gerrit uses this to "hide a handful of projects on an otherwise public server"; in gitolite you'd better avoid giving R = @all in the first place :)

• Update 2010-10-24: as per this Gerrit now has read access control at the branch level -- they can afford to do that because they have a full jgit stack to play with. Even then it was not easy -- they had to implement a callback from jgit to gerrit for the fetch, and deal with evil clients that might try to read an object by pushing a supposed change on top of a SHA that they know but don't actually have. (You'll have to think about this carefully; it may not be immediately obvious to people who do not know the ref-exchange in the git protocol).

  Gitolite is dependent on git itself to provide that -- it just cannot be done without support from git core. I can see some corporates drooling at this possibility (makes no sense for open source projects IMO) ;-)

  My normal recommendation is to use separate repos if you really need this while continuing to use gitolite. Much simpler and easier to audit and to convince auditors that "those people can't see that code".

Categories:

• gitolite doesnt have an "owner" for each project in any administrative sense. Perhaps you could consider whoever has RW+ perms to be an owner but it doesn't go beyond what that implies.

• gitolite doesnt do anything special to signed or annotated tags

• Force push is the same as delete by default. However, gitolite can now allow these two separately if that's how you need it.

  Of course, direct pushing clashes with code review, and gerrit recommends that if you want code review you should not use this feature. [Normal pushes in gerrit go through a temp branch that is moved to the correct one after a review is done; direct pushes are all that gitolite has].

• author/committer identity: checking these fields in pushed commits is likely to be important in some projects, but gitolite doesn't have any notion of this. Hmm... I smell another feature in the future :)

The rest of it is in areas that the two tools have no overlap on (again, code review being the main thing), or, as I said at the top, features that both tools have.