Thoughts on Linus Torvalds’s Git Talk

December 12, 2007 Joe Moore

At Pivotal Labs last week we watched Linus Torvald’s Google talk about Git, the Source Code Management (SCM) system he wrote and uses to manage the Linux kernel code.

I’ve watched it twice now and here are some thoughts, based on quotes and themes from the video.

“I Never Care About Just One File”

Linus stated that one of the reasons Git was wonderful for him is that, as a high level code maintainer, he needs to merge thousands of files at once. In fact, he stated that he never cares about just one file.

Not so for me. As an in-the-trenches developer, my whole life is caring about just one file, over and over again. When I merge, I care about each file because, since I work on small teams and with small codebases, there is a fairly high likelihood that my changes will collide with those from another developer.

“The Repository Must Be Decentralized…. You Must Have a Network of Trust”

Linus made the point that central repositories suck for large projects where the morons must not have commit access — only the super privileged are allowed to commit code back to the repo. He argues that Git is better because it is a decentralized network of repositories — there is no central master, only Some Dudes who have repositories. Usually there is Some Dude In Charge, like Linus, and everyone tends to pull code from them. To update the “master” code version, Some Dude In Charge pulls code from the repositories owned by Some Other Wicked Smart Dudes, who have most likely pulled code from Some Other Trusted Dudes (And One Gal), and so on. Thus, rather than limit access to just the hand-selected few, everyone has their own local copy of the repository, and the smart merge from the smart who merge from the smart, resulting in some kind of official or de facto version.

While I like the local copy of the repo idea, Pivotal does not work the way Linus describes… but Pivotal is weird, in a good way. We all have full commit rights. Our network of trust is everyone. The Dude In Charge is named Continuous Integration. CI makes the official versions. CI runs the tests. CI makes sure that the deploy process works. I’m sure that we could coerce Git into working in a centralized-like way, where it merges automatically from the individual developers and runs the builds, but I’m not sure if that would be forcing a square peg into a penguin-shaped hole.

“Some Companies Use Git And Don’t Even Know It”

Linus described how developers at some companies use Git on their development machines, committing their changes and merging fellow developer’s changes with Git, then pushing those changes to central SVN repos. He rather mocked this, but it actually sounds like a good solution: developers merge, so use the tool that’s good at that. CI machines and deploy machines love centralized master repositories, so use that for those jobs.

“It Does Not Matter How Easy It Is To Branch, Only How Easy It Is to Merge”

Well said. I never thought about that before but he is completely right. I could never put my finger on why I never branch in SVN, even though it’s practically ‘free’ and easy to do. Now it’s obvious: who cares how easy it is to branch when merging sucks? Git is supposed to make merging incredibly easy because Git is content-aware rather than just file-aware… or something like that. I’ll believe it when I see it, but if Git really does make merging highly divergent branches easy then I’ll give it a try.

Joe’s Take

I’d like to try Git, especially if it makes branching and merging those branches as easy as Linus suggests, but I don’t think that Pivotal would get as much benefit out of it as large, distributed open source projects. A ‘really big’ project might have 10 developers, not thousands, and all must have commit rights. Our network of trust goes like this: if you are here, we trust you; if we don’t trust you, you have to leave. And the idea of having to merge directly from my fellow developers sounds like a pain in the ass… why would I want to merge from 3 separate pairs when I can pull code from the central repo and be reasonably sure (thanks to CI) that it is clean and green? Hopefully I’ll be able to answer those questions soon by using Git on a project.

(Note: originally posted on my personal blog at http://40withegg.com/2007/12/11/thoughts-on-linus-torvalds-s-git-talk)

About the Author

Biography

More Content by Joe Moore
Previous
Collapsing Migrations
Collapsing Migrations

(6:30 pm: updated to use mysqldump) (12/14/07: updated to remove db:reset since the Rails 2.0 version now d...

Next
OpenSocial
OpenSocial

Okay, it's not ready for prime time. But it was entertaining digging into OpenSocial and making some gadget...