Subversion Best Practices

This is a quick set of guidelines for making the best use of Subversion in your day-to-day software development work.

Use a sane repository layout

There are many ways to lay out your repository. Because branches and tags are ordinary directories, you'll need to account for them in your repository structure.

The Subversion project officially recommends the idea of a "project root", which represents an anchoring point for a project. A "project root" contains exactly three subdirectories: /trunk, /branches, and /tags. A repository may contain only one project root, or it may contain a number of them.

Book reference: Choosing a Repository Layout.

Commit logical changesets

When you commit a change to the repository, make sure your change reflects a single purpose: the fixing of a specific bug, the addition of a new feature, or some particular task. Your commit will create a new revision number which can forever be used as a "name" for the change. You can mention this revision number in bug databases, or use it as an argument to svn merge should you want to undo the change or port it to another branch.

Book reference: Changesets.

Use the issue-tracker wisely

Try to create as many two-way links between Subversion changesets and your issue-tracking database as possible:

Track merges manually


When committing the result of a merge, be sure to write a descriptive log message that explains what was merged, something like:

Merged revisions 3490:4120 of /branches/foobranch to /trunk.

Book reference: Tracking merges manually, and Merging a whole branch to another.

Understand mixed-revision working copies

Your working copy's directories and files can be at different "working" revisions: this is a deliberate feature which allows you to mix and match older versions of things with newer ones. But there are few facts you must be aware of:

  1. After every svn commit, your working copy has mixed revisions. The things you just committed are now at the HEAD revision, and everything else is at an older revision.
  2. Certain commits are disallowed:
  3. svn update will bring your entire working copy to one working revision, and is the typical solution to the problems mentioned in point #2.

Book reference: Mixed-revision working copies.

Be patient with large files

A nice feature of Subversion is that by design, there is no limit to the size of files it can handle. Files are sent "streamily" in both directions between Subversion client and server, using a small, constant amount of memory on each side of the network.

Of course, there are a number of practical issues to consider. While there's no need to worry about files in the kilobyte-sized range (e.g. typical source-code files), committing larger files can take a tremendous amount of both time and space (e.g. files that are dozens or hundreds of megabytes large.)

To begin with, remember that your Subversion working copy stores pristine copies of all version-controlled files in the .svn/text-base/ area. This means that your working copy takes up at least twice as much disk space as the original dataset. Beyond that, the Subversion client follows a (currently unadjustable) algorithm for committing files:

So while there's no theoretical limit to the size of your files, you'll need to be aware that very large files may require quite a bit of patient waiting while your client chugs away. You can rest assured, however, that unlike CVS, your large files won't incapacitate the server or affect other users.

Know when to create branches

This is a hotly debated question, and it really depends on the culture of your software project. Rather than prescribe a universal policy, we'll describe three common ones here.

The Never-Branch system

(Often used by nascent projects that don't yet have runnable code.)

Pros: Very easy policy to follow. New developers have low barrier to entry. Nobody needs to learn how to branch or merge.

Cons: Chaotic development, code could be unstable at any time.

A side note: this sort of development is a bit less risky in Subversion than in CVS. Because Subversion commits are atomic, it's not possible for a checkout or update to receive a "partial" commit while somebody else is in the process of committing.

The Always-Branch system

(Often used by projects that favor heavy management and supervision.)

Pros: /trunk is guaranteed to be extremely stable at all times.

Cons: Coders are artificially isolated from each other, possibly creating more merge conflicts than necessary. Requires users to do lots of extra merging.

The Branch-When-Needed system

(This is the system used by the Subversion project.)

Pros: /trunk is guaranteed to be stable at all times. The hassle of branching/merging is somewhat rare.

Cons: Adds a bit of burden to users' daily work: they must compile and test before every commit.