All good things come to an end: Challenges in migrating 16 years of research software history from SVN to git

Abstract

At DLR we have developed the open source software RCE since 2006, using SVN for version control. RCE is a research software developed by a team consisting of only four researchers, fulfilling all tasks in a research software's life-cycle, i.e., development, testing, maintenance, project acquisition and support, and scientific work. In 16 years of development, RCE has accumulated over 30,000 commits made by dozens of contributors. Moreover, we use deeply integrated processes for issue management, continuous integration and testing. While SVN has served us well over the years, the current de facto standard for version control is git, which offers many benefits for the development process. Therefore, we faced the task of migrating our codebase from SVN to git. This has presented us with a challenge that was not fully covered by known good practices and off-the-shelf tools, due to the size of the code repository, the intertwined accompanying processes, and the limited resources available.

In this talk, we present the obstacles we encountered, and the respective decisions we made to migrate a large software project with the limited resources of a small research team. For instance, we illustrate how we adapted well-known branching models for our use case. Moreover, we present our toolchain, based on KDE's svn2git for executing the migration, which vastly outperforms a "git svn"-based migration. Finally, we briefly illustrate the challenges faced in adapting our use of the Jenkins continuous integration and Mantis bug tracker tools to a git-based development platform.