Sunday, April 24, 2011

Three reasons to avoid Subversion

I've been using CVS for most of the last 15 years. I came to the Subversion party late. Despite all my friends saying how wonderful it was, I didn't use it professionally until 2009.

Initially, I was reasonably happy with it but over time I have come to see the wisdom of Linus Torvalds statement that Subversiom is "the most pointless project ever started."

Reason #1
The integration with Eclipse is patchy. No matter how great the tool, if the integration with your IDE of choice is buggy then avoid it unless absolutely necessary.

Eclipse sometimes says I have checked everything in when I haven't. It says I have sometimes checked everything out when I haven't. It can get confused during merges - especially if you have been moving files around. And this seems to be the case over a number of versions of Eclipse I have used in the last 2 years (most recently Helios) using both Subversive and Subclipse plugins. A few members of my team and I have been forced to avoid Eclipse altogether and use the Tortoise Subversion plugin.

When Subversion gets its knickers in a twist, it's harder to manually edit the metadata files in the .svn directory since they appear to be binaries. With CVS, they were plain text files. Of course, it's always nasty to do this. But sometimes, you just gotta.

Reason #2
Subversion can have old JARs stored in the .svn directories. As an example, I picked a random project from my hard drive (Gilead) and looked in the .svn directory.

phillip:1.3.1-SNAPSHOT henryp$ pwd
phillip:1.3.1-SNAPSHOT henryp$ jar -tf .svn/text-base/comet4gwt-1.3.1-20100205.214253-2.jar.svn-base | more

So, a living, breathing JAR in the metadata directory!

You might ask: "so what?". Well, this caused a lot of confusion on a project that loaded all its JARs into the classpath using a shell script that used a wild card. (Yes, I know that is bad practise in these days of OSGi et al but bad practices are unfortunately part of life and probably will continue to be until we are a regulated profession...) For a few hours, we were wondering why classes from a library that had long since been removed were showing up in our code.

Reason #3
When a friend breathlessly told me about Subversion, he said you could move files around and Subversion would understand. Poor CVS simply saw it as one file being deleted and another being created.

Well, this is not the entire story. If you move a file, the change history can move with it and that's about it.

“A lesser-known fact about Subversion is that it lacks “true renames”—the svn move command is nothing more than an aggregation of svn copy and svn delete.”
Version Control with Subversion (For Subversion 1.5, r3305) p106

This may be tolerable for just one or two classes. But, let's say you need to do a major refactoring. I'm sure you've been here before:

"Files and directories are shuffled around and renamed, often causing great disruption to everyone on the project. Sound like the perfect case for a branch, doesn't it? Just create a branch, shuffle things around, then merge the branch back into trunk, right?

"Alas, this scenario doesn't work so well right now and is considered one of Subversion's current weak spots."
Version Control with Subversion

“The moral of this story is that until Subversion improves, be very careful about merging copies and renames from one branch to another.”
Version Control with Subversion (For Subversion 1.5, r3305), p107

I found during a recent mass-refactor that if I moved a file then moved the file again (having not checked in until I was satisfied), Subversion would simply panic.

Subversion will not fulfill the dream of having many branches where you can refactor to your heart's content and merge later. If you want that, try another tool (I'm starting to get interested in Git).

The bottom line is that Subversion is only useful if you have one branch that's in production and one development branch. This is OK for many projects. But if you are working on a project that has teams from New York to London to Bangalore working on different product lines as I am currently, I'd strongly recommend that you avoid it.

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