Source Control HOWTO: Repositories

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checkbox is almost irresistible. It simply begs to be checked, even though it is very rarely the right thing to do.

When we first designed the obliterate command for Vault, I wanted its user interface to somehow make the user feel guilty. I argued that the obliterate dialog box should include a photograph of a 75-year old catholic nun scowling and holding a yardstick.

The rest of the team agreed that we should discourage people from using this command, but in the end, we settled on a less graphical approach. In Vault, the obliterate command is available only in the Admin client, not the regular client people use every day. In effect, we made the obliterate command available, but inconvenient. People who really need to obliterate can find the command and get it done. Everyone else has to think twice before they try to rewrite history and pretend something never happened.

Kimchi Again?
Recently when I asked my fifth grade daughter what she had learned in school, she proudly informed me that " everyone in Korea eats kimchi at every meal, every day." In the world of a ten-year-old, things are simpler. Rules don't have exceptions. Generalizations always apply.

This is how we learn. We understand the basic rules first and see the finer points later. First we learn that memory leaks are impossible in the CLR. Later, when our app consumes all available RAM, we learn more.

My habit as I write these chapters is to first present the basics in a "matter of fact" fashion, rarely acknowledging that there are exceptions to my broad generalizations. I did this during the chapter on checkins, failing to mention the "edit-merge-commit" until I had thoroughly explored "checkout-edit-checkin."

In this chapter, I have written everything from the perspective of just one specific architecture. SCM tools like Vault, Perforce, CVS and Subversion are based on the concept of a centralized server which hosts a single repository. Each client has a working folder. All clients contact the same server.

I confess that not all SCM tools work this way. Tools like BitKeeper and Arch are based on the concept of distributed repositories. Instead of one repository, there can be several, or even many. Things can be retrieved or committed to any repository at any time. The repositories are synchronized by migrating changesets from one repository to another. This results in a merge situation which is not altogether different from merging branches.

From the perspective of this SCM geek, distributed repositories are an attractive concept. Admittedly, they are advanced and complex, requiring a bit more of a learning curve on the part of the end user. But for the power user, this paradigm for source control is very cool.

Having no experience in the implementation of these systems, I will not be explaining their behavior in any detail. Suffice it to say that this approach is similar in some ways, but very different in others. This series of articles will continue to focus on the more mainstream architecture for source control.

Looking Ahead
In this chapter, I discussed the details of repositories. In the next chapter, I'll go back over to the client side and dive into the details of working folders.


Eric Sink is a software developer at SourceGearwho make source control (aka "version control", "SCM") tools for Windows developers. He founded the AbiWord project and was responsible for much of the original design and implementation. Prior to SourceGear, he was the Project Lead for the browser team at Spyglass (now OpenTV) who built the original versions of the browser you now know as

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