gdritter repos documents / f398fd7
Started distributed git draft Getty Ritter 8 years ago
1 changed file(s) with 77 addition(s) and 0 deletion(s). Collapse all Expand all
+77
-0
posts/distributed-git.md less more
1 We used to use centralized version control systems, like SVN. Those
2 had a single _canonical_ version of the repository, and multiple
3 scattered copies that are "checked out" from the central repo. You
4 synchronize your current state with that repo, make some changes,
5 and "push" those changes back to the central repo.
6
7 Now, most of the computing industry has switched over to
8 decentralized version control systems, like mercurial or git. In
9 these, any repo can pull from any other: if you and a friend are
10 collaborating on a project, and both of you have publicly visible
11 repositories, you can ping your friend to tell them about new
12 changes you've made and they can pull them from you, and then
13 they can make further changes and you can pull from them. In
14 this setup, there is no "central repository", at least in the
15 technical sense. If this project grows, it's probably a good
16 idea to choose one person's repo to be the "canonical" one, but
17 as far as the _underlying technology_ is concerned, it's just another
18 copy: it's only special in a _social_ sense.[^push]
19
20 [^push]: I'm aware that I'm ignoring _pushes_ here: you could also use
21 git and friends basically the same way you would SVN, by having a
22 central repository that everyone pull from and pushes to. This is
23 true, but what's interesting about distributed version control is
24 that you don't _have to_ do so. In fact, the situation I'm talking
25 about, you would probably have at least four repos: two of them
26 on servers with a stable, addressable location, and two or more
27 on local machines being worked on. Each server copy acts kind of
28 like a 'central' copy for the programmer who owns it, and the
29 pulls go back between them.
30
31 Github and similar services were built to support this paradigm: I
32 can create a repository, and anyone who wants can go in and, with
33 a click, _fork_ the repository, which copies it into their own
34 namespace. You can pull changes from one or the other, or notify
35 someone that you have changes you'd like them to consider with
36 a _pull request_[^pr]. Github tends to think of the original copy
37 of a repo as "canonical", but that's merely a convention.
38
39 [^pr]: I'd argue this is a poor piece of terminology: the phrase
40 is ambiguous enough that I originally believed it had something
41 to do with asking permission to clone someone's work. I've heard
42 the alternative phrase _merge request_ used, which has the problem
43 that it's less accurate to the underlying abstraction—it may or
44 may not incur a merge in Git's sense—but it _does_ hint at the
45 actual operation happening a bit more. I'm open to alternatives!
46
47 On the other hand, Github itself is _not_ decentralized: it offers
48 a centralized toolset for managing a decentralized technology.
49 This gets criticized regularly, especially when Github has a major
50 outage and programmers all around the world can't get work done.
51 Github also offers more tooling on top of just repo hosting and
52 management: project wikis, issue tracking, commenting in various
53 places, and so forth. So let's think about what a distributed
54 _Github_ would look like.
55
56 # A Programmer's View
57
58 Let's call our distributed Git software _GitNode_.
59
60 Say I run an instance of GitNode on my personal web server at
61 `http://gitnode.gdritter.com/`: this server contains copies of
62 all the git repos I care about, and the GitNode server is aware
63 of them, so if nothing else it gives me a nice browsable view of
64 the state of the repo, past commits, and so forth.
65
66 My friend _also_ runs an instance of GitNode at
67 `http://gitnode.example.com/`, and they have a repo I want to
68 work on called `my-project`. There are two ways I can do this:
69
70 - I can go to my own GitNode instance and tell it the location
71 of the repo I want to clone: that is, point it to
72 `gitnode.example.com:my-project`, and it'll clone it for me.
73 I could also write a bookmarklet or browser plugin to make this
74 easier, to avoid having to retype or copy/paste things in.
75 - I could also _perform a visit_ to my friend's GitNode instance.
76 I navigate to `gitnode.example.com` and click a _Visit_ button,
77 which