Boy Meets World

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Sat, 17 Mar 2007

This is an archived blog post. I've switched to using WordPress as my blogging software and have not migrated all my old posts. I believe strongly in not letting an old link die, so this page continues to work. Please do visit mikemason.ca/blog to read newer posts.

CVS to Subversion Experience Report

My current client in Calgary recently switched from CVS to Subversion. Our main goal for switching was to fix performance problems with CVS, but we also hoped to get some benefit from the improved features within Subversion. The CVS repositories were on a reasonably beefy Sun box but we’d been seeing “waiting for lock” messages and frequent hanging of our CVS clients. The server didn’t look like it was under load and switching the repositories to their own mount point didn’t fix the problem. One of the teams also wanted to clean up their branching structure–after five years of CVS they were in a bit of a mess.

Our first conversion was straightforward. We wanted to convert a recent project from its existing home in a CVS module into Subversion. We used cvs2svn to do the conversion and ended up with around 6,000 revisions in Subversion. This represented about 18 months of effort from about a dozen developers, and the conversion took about 2 hours to run. The team’s developers had been briefed on the conversion and all checked in to CVS beforehand, then checked out from Subversion once we were ready. The entire team–including business users, analysts and testers–upgraded from TortoiseCVS to TortoiseSVN and pretty much carried straight on with their work.

We got the performance improvement we had hoped for, with a Subversion update taking around ten seconds compared to CVS’ one or two minutes. This is with the repository on the same Sun server, the only thing we needed to do was actually install the Subversion software.

The second conversion was more complicated. We wanted to take a 5GB CVS repository with five years of history and not only upgrade to Subversion, but sort out some branching problems. One of the branches within CVS had started out as a release branch but evolved into its own product maintained by a separate team. We also had a fairly complicated set of branches we didn’t want to include, tags that were no longer worthwhile, etc. We scripted the conversion by customizing the example cvs2svn-example.options file included with cvs2svn to get exactly what we wanted. The big “Eureka!” moment came when we realized that promoting the CVS branch to its own product was really easy once everything was in Subversion. cvs2svn converts branches and puts them into their own directory, but there’s nothing stopping us from moving a directory within Subversion. We simply copied the branch-that-is-a-product into a higher level, mirroring a regular project’s structure, then deleted its old location so developers wouldn’t get confused about which was the right one.

Converting the 5GB, five year old repository took around 16 hours over a weekend. Shuffling directories around once converted took only a few minutes, and we used the excellent TortoiseSVN Repository Browser so all our move operations ran directly against the repository and were lightning fast.

Posted 15:42, 17 Mar 2007.

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