Git: The Lean, Mean, Distributed Machine

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  • 1. Chris Wanstrath hi everyone, i’m chris wanstrath. how many people here use git?
  • 2. i play guitar i have a schecter classic similar to this. mine is prettier.
  • 3. i’m from cincinnati ohio
  • 4. but live in san francisco
  • 5. i started as a lowly paid consultant
  • 6. Then I worked at CNET then worked at CNET for a few years
  • 7. Then I worked at CNET (which is now owned by CBS)
  • 8. Then I was a highly paid consultant after that i became a highly paid consultant
  • 9. before co-founding github
  • 10. git The Lean Mean Distributed Machine By Chris Wanstrath anyway, i want to talk a bit about git today
  • 11. if we’re going to talk about git, we need to start by talking about source control management (SCM) or version control
  • 12. basically version control is like wikipedia
  • 13. for your code
  • 14. you use it to see what changes others made
  • 15. inspect those changes
  • 16. and contribute your own
  • 17. git? who uses token promo slide
  • 18. these companies use git
  • 19. and so do these open source projects
  • 20. let’s briefly go through the history of open source SCMs (at least the ones we care about)
  • 21. Revision Control System (RCS) was written in the early 80s and used to store history on a file by file basis. A directory of source code could contain many RCS repositories, each concerning itself with a single file. it’s like a hut - very basic, primitive even, but works great when all you need is shelter Later that decade, a professor began working with two grad students on a C compiler (in the name of scholarly pursuits). As they began using RCS, the professor noted a number of limitations. It was difficult to share files, and even more difficult to share entire projects.
  • 22. So, they wrote CVS - the Concurrent Versioned System - and released it as open source in the early 1990s. Concurrent because it allowed multiple individuals to collaborate on a project together, without stepping on each other's toes, and versioned system because it was initially a collection of RCS repositories with network awareness. CVS was like a cabin. better than a hut, but still pretty crappy it worked well for a while, but there were limitations. Dealing with directories was difficult, and much different than the way one would normally deal with directories in Unix.
  • 23. Ten years later (see a pattern?) a new revision control system was released, called Subversion (or SVN). Subversion was intended to replace CVS by improving on CVS. History, directories, deletions, and other CVS warts were fixed. mod_dav integration was included, as well as anonymous checkout. (Anonymous checkout in CVS was literally a hack added by the OpenBSD.) Subversion was not subversive, but it did work well enough. Many felt it a welcome relief and hurriedly switched. Big, lumbering organizations spent years converting their repositories to SVN. IDEs and editors included Subversion integration. it was like a house, same idea but much better than a cabin
  • 24. Server Committer Committer Committer this is the rcs / cvs / svn model.
  • 25. Server Committer Committer Committer someone commits to the server
  • 26. Server Committer Committer Committer and everyone else pulls down the changes
  • 27. this is bad why?
  • 28. Server first off, the server is the babysitter
  • 29. “The Subversion ser ver’s down” SVN’s down! you can’t do anything without the server’s permission
  • 30. second, low visibility into your coworkers and subordinates’ activity.
  • 31. at cnet, we used bugzilla. it was awesome (as you can see)
  • 32. we’d also get diffs emailed to us after each commit
  • 33. because our group was large, and fluid, i’d often get commits emailed to me i didnt care about
  • 34. or understand
  • 35. this meant i spent extra time throwing away junk
  • 36. emails that come to me should be for me
  • 37. Trac if you’re lucky, you use trac to watch what everyone is doing. it has rss and is a bit smarter. usually you have to set it up yourself
  • 38. another problem: your subversion workflow is single threaded it’s hard to stop working on a feature to quickly fix a bug without losing your feature’s changes changed files are either committed or discarded well, not entirely true...
  • 39. you could always use a branch but that sucks, and big changes are usually disasters i once worked on a project for 3 months where we worked on a massive new feature
  • 40. as it neared completion, we had a big meeting
  • 41. a 2 hour meeting
  • 42. there we decided how to merge in the changes from our branch to trunk it was one of the worst meetings ever
  • 43. and i’ve been in some bad meetings
  • 44. one person was assigned with the task of merging the branch and trunk
  • 45. he was merging and fixing bugs in code he did not write
  • 46. or understand
  • 47. it did not go well
  • 48. another problem with the ‘babysitter’ model is that experimentation is difficult
  • 49. all your experiments are public
  • 50. everyone sees everything you commit
  • 51. solution? don’t commit at least, that was my solution
  • 52. and that’s just work stuff the centralized model, when applied to open source, is a huge pain it’s difficult to maintain patched versions of open source independently if a project dies on the internet, does anyone care?
  • 53. what’s the answer? dvcs! git! happy!
  • 54. git was started by linus torvalds a DVCS built as an efficient content addressable file system
  • 55. the guy who started the linux kernel
  • 56. if rcs is a hut
  • 57. cvs is a cabin
  • 58. and subversion is a house
  • 59. git is a castle
  • 60. or a ninja
  • 61. or shaq
  • 62. Server Committer Committer Committer the thing that makes git, and all distributed version control systems like it different, is the idea that it’s “distributed” take this centralized model
  • 63. Server Committer Committer Committer and make every copy of the code its own, full fledged repository any copy can accept or create commits. anyone can pull commits from any copy.
  • 64. Server Committer Committer Committer now you can push to the server
  • 65. Server Committer Committer Committer or committers can push and pull from each other
  • 66. Server Committer instead of “checking out” code
  • 67. Server Committer you “clone” or copy a repository
  • 68. if github explodes, you don’t lose any code
  • 69. Server Server Server Committer in fact, because you have a full copy of your repository at all times, you don’t need to tie yourself to a single remote repository
  • 70. you can push to as many servers as you want
  • 71. another word for ‘clone’ or ‘copy’ is ‘fork’
  • 72. it may seem like anarchy at first but sane and useful workflows have evolved
  • 73. #1 in fact, the first workflow i want to talk about is called Anarchy
  • 74. Server Committer Committer Committer you remove the server
  • 75. Committer Committer Committer then make everyone a peer
  • 76. Committer Committer Committer then take away commit access from each other
  • 77. Coder Coder Coder and you end up with repositories floating in the void this is how the internet works, or how git works by default
  • 78. Coder Coder Coder everyone pushes and pulls from each other, managing their own version of the code for small projects with very few contributors, it works fine and it would work great on small, experimental projects inside of any organization (you just need a place to publish your changes)
  • 79. an example of this, let’s say i was on github and i wanted to add a patch to schacon’s ticgit
  • 80. i’d click the fork button
  • 81. i now have a copy of schacon’s ticgit called defunkt’s ticgit now i can make changes and ask scott to check them out. if he likes them, he’ll merge them in if he doesn’t like them, oh well. i can still use them in my project and keep up to date with his changes. someone can come along and fork from me if they want, too
  • 82. #2 blessed but anarchy doesn’t scale the second workflow is called Blessed
  • 83. Coder Coder Coder Coder the blessed workflow has the same basic idea as Anarchy
  • 84. Blessed Coder Coder Coder but one of the repositories is the Blessed repo
  • 85. Blessed Coder Coder Coder everyone takes their cues from the blessed repository its development is considered the mainline, or trunk deploys and packages are pushed from the blessed repo
  • 86. Blessed Coder Coder Coder others can still push and pull from each other, remember
  • 87. in the business world this works great for dealing with contractors
  • 88. Blessed Coder Coder Coder don’t give them push access, just pull access
  • 89. Blessed Coder they pull down your code, make their changes, then tell you when the changes are ready
  • 90. Blessed Coder if you like what you see, you merge in the contractor’s changes the contractor never has direct write access to your company’s code
  • 91. if there were a bunch of us working on ticgit, scott’s may be the Blessed repository he started the project and is in charge of merging in all changes. we all watch his changes
  • 92. this is how rails works rails/rails is the Blessed repository, from which the gems are built and david controls. we all follow this repo’s development and treat it as “official” by convention only
  • 93. this is also how rentzsch’s click to flash works click to flash is an amazing safari plugin that disables flash, similar to the firefox extension
  • 94. it was forked from google code and has been given a life of its own on github, under rentzsch’s guidance. contributors fork his repository and he merges in good changes. the plugin’s development has been a perfect example of how distributed version control puts the power in the hands of the developer, not the server
  • 95. #3 lieutenant the next workflow is called ‘lieutenant’ - great for massive projects, like the kernel
  • 96. Blessed Lieutenant Lieutenant Coder Coder Coder Coder in this model, there is a blessed repository and a few designated lieutenants the lieutenants are people trusted by the blessed repository
  • 97. Blessed Lieutenant Lieutenant Coder Coder Coder Coder coders will pull from a lieutenant, make their changes, then request the lieutenant merge in their changes
  • 98. Blessed Lieutenant Lieutenant Coder Coder Coder Coder lieutenants are usually in charge of a specific subsystem or part of the large system if they like the change, they will pull it in
  • 99. Blessed Lieutenant Lieutenant Coder Coder Coder Coder they’ll then inform the blessed repository that they have changes which need to be merged in the blessed repo, trusting the lieutenant, pulls in the changes
  • 100. Blessed Lieutenant Lieutenant Coder Coder Coder Coder this is typically coordinated over a mailing list
  • 101. this is the kernel’s model
  • 102. #4 centralized finally the centralized model, one repository acts as the ‘server’
  • 103. Server Committer Committer Committer this mimics the traditional babysitter model but you only need your babysitter to pull and push changes - branches and commits can still be created locally whenever
  • 104. Server Committer Committer Committer the server being down does not dramatically hamper your work
  • 105. Server Committer Committer Committer yet the flow stays mostly the same
  • 106. Deploy Server Committer Committer Committer the central server, as in the old model, can also be used to deploy
  • 107. Staging Production Committer Committer Committer and staging servers can easily be setup
  • 108. git isn’t all about distributed servers in fact, one of the best parts about git is its branching support
  • 109. branches are local, incredibly lightweight, and easy to switch between it’s easy to devote each branch to a single feature or bug we call these ‘topic branches’
  • 110. $ git checkout -b bug_2342 from your working directory you just made a new branch
  • 111. buckets of different things because branches are so cheap, you can keep around buckets filled with experiments, new ideas, or new features no one will ever see them unless you want them to be seen
  • 112. Staging Production Committer Committer Committer this changes the staging server idea
  • 113. Feature A Production Feature B Committer Committer Committer you may start to have topic staging servers where you boot up staging for a single branch and test out a new feature, no more generic ‘staging’ branch - each person may even have their own staging server
  • 114. Coder because every copy is its own repository, we are given the freedom to structure our workflows socially rather than technically
  • 115. Team A Team B it’s easy to have multiple small teams, move people between projects, and monitor multiple projects no need for one monolithic subversion server - git repositories are a breeze to setup
  • 116. with something like github, watching your team’s development is trivial. do it with rss...
  • 117. or with a service you’re already comfortable using integration with campfire, email, fogbugz, lighthouse, friendfeed, twitter, etc
  • 118. the site also lets you comment on commits, providing dead simple and effective code review git and github are what we use in our private client work and on our own websites, as well as for our open source
  • 119. as far as git IDE support, the textmate ProjectPlus extension shows you the status of tracked files right in the drawer
  • 120. there’s also a git textmate bundle available on github
  • 121. if you’re an eclipse user, the egit plugin lets you commit to, manage, and track git repositories from within eclipse it’s written using jgit, a pure-java implementation of git
  • 122. emacs people can use DVC which aims to provide a common interface for all distributed version control systems there’s also a git mode
  • 123. or my person favorite, magit
  • 124. if you use os x, an open source program called GitX is under active development
  • 125. which is based on the cross platform Git-GUI
  • 126. for OS X there’s also GitNub which isn’t as actively developed
  • 127. as far as libraries go, a search for ‘git’ on github returns almost 3000 unique repositories darcs or hg to git converters, git vim projects, git in .NET, even blogs and wikis based on git
  • 128. remember when i said git was a content addressable file system? well, it’s true this is gist. it’s a git powered pastie
  • 129. you paste in code and share it with coworkers or friends
  • 130. but the best part are these clone URLs i can check out a pastie i made, make changes, then push a new version
  • 131. these are the revisions you can’t tell the difference between changes i made on the web and changes i made locally then pushed
  • 132. this kind of stuff is the future imagine a distributed, versioned wiki or documentation project or book a distributed, versioned bug tracker a distributed, versioned chat application
  • 133. in fact, a number of books are already being written on github
  • 134. scott’s book is being translated right now
  • 135. a distributed, versioned everything
  • 136. this has been a fairly basic overview of git for more information, check out
  • 137. thanks questions?
  • 138. flickr
  • 139. flickr