We are happy to announce that Project Hosting on Google Code now supports the Mercurial version control system in addition to Subversion. This is being initially rolled out as a preview release to a few invited users on a per-project basis, so that we can iron out the kinks before making this available to the general public.
Mercurial, like Git and Bazaar, is a distributed version control system (DVCS) that enables developers to work offline and define more complex workflows such as peer-to-peer pushing/pulling of code. It also makes it easier for outside contributors to contribute to projects, as cloning and merging of remote repositories is really easy.
While there were several DVCSs that we could support, our decision to support Mercurial was based on two key reasons. The primary reason was to support our large base of existing Subversion users that want to use a distributed version control system. For these users we felt that Mercurial had the lowest barrier to adoption because of its similar command set, great documentation (including a great online book), and excellent tools such as Tortoise Hg. Second, given that Google Code's infrastructure is built for HTTP-based services, we found that Mercurial had the best protocol and performance characteristics for HTTP support. For more information, see our analysis.
If you would like to help us launch Mercurial and to try out the features as an invited user, please fill out the following form. We are currently looking for active projects with more than two users that are willing to try out Mercurial and work with us to identify issues and resolve them. For projects that plan on migrating from Subversion, see our conversion docs for the steps required for this process.
Our implementation of Mercurial is built on top of Bigtable, making it extremely scalable and reliable just like our Subversion on Bigtable implementation. For more information on our Mercurial implementation, we will have a TechTalk at Google IO that will be led by Jacob Lee, one of the core engineers working on Mercurial support. Let us know if you plan on attending and we'll give you access to Mercurial ahead of the talk.