Version control

PDF version

Git resources

  • Pro Git book by Scott Chacon. Available online (gratis) or paper. I suggest working through at least chapters 1–3. We’ll also pick up some things from chapters 7–8 later in the course.
  • Understanding Git Data Model article by Zvonimir Spajic. Great intro to the three types of objects: blobs, trees, and commits. Part of a series.
  • Oh Shit, Git! is a fun overview and printable cheat sheet/booklet available for $10. (There’s also a version without explicit language, if you prefer.)

git_commit.png

Figure 1: xkcd on git commit messages

Purpose

  • We have files that represent code, configuration, documentation.
  • Need tools to manage modifications
  • Team environment means that multiple devs may edit the same file(s). Need to be careful about integrating changes.
  • However, VC even useful for a lone developer: to see previous versions, undo changes, redo, manage different configurations, etc.

History

Although git’s model of snapshot-based, concurrent, and distributed version management is now dominant, it can be useful to understand some of the other design points that were used in the past.

Snapshots vs deltas

  • One way that VC tools differ: do they manage snapshots of your files, or do they manage changes (aka deltas or diffs) to files?
    • Either store original and forward deltas,
    • Or store most recent and reverse deltas.
  • Git (and friends) instead store snapshots – every version of every file. Faster to find old versions compared to applying deltas.
  • Does take up more space than delta-based versions. Can use compression to reduce space.

Centralized vs distributed

  • Centralized means there’s some designated server that keeps all the history.
  • Centralized also means browsing the history or adding to it requires network access to the server.
  • Distributed means each developer has their own copy of the entire history.
  • Distributed also means I can work while disconnected and then later push/pull.
  • A distributed VC can also be a much-improved centralized VC.
  • GitHub/GitLab are central servers for a distributed tool.

Winner: snapshots and distributed

  • git (free/OSS) – GitHub (commercial)
  • mercurial
  • bzr “bazaar”
  • BitKeeper