Migrating a SVN repo to Git, part deux: SubGit to the rescue

  1. Migrating a SVN repo to Git: a tale of hacking my way through
  2. ➤ Migrating a SVN repo to Git, part deux: SubGit to the rescue

To improve is to change; to be perfect is to change often.
— Winston Churchill

In my previous post about SVN→GIT conversion I’ve described steps to convert a nested SVN repo to GIT using svn2git, svndumpfilterIN, SVN::DumpReloc and some manual editing of SVN dump files.

This process worked fine for smaller repos, but after some threshold I’ve hit the wall: final conversion with svn2git for one of the larger repos was taking 5 days and was never quite finished because of Windows version of Git crashing in the middle of process. Those crashes were related to Cygwin’s implementation of fork which requires some address space to be reserved for Cygwin heap and 5 days long run was exhausting those addresses.

After a couple of attempts to convert a repo (which took about 2 weeks!), I’ve realized that I need a more robust and preferably faster solution. And that’s when I finally found SubGit!

SubGit is a tool for a smooth, stress-free SVN to Git migration. Create writable Git mirror of a local or remote Subversion repository and use both Subversion and Git as long as you like. You may also do a fast one-time import from Subversion to Git or use SubGit within Atlassian Bitbucket Server.

SubGit is a commercial closed-source Java application. Fortunately, it’s free for one-time conversions and mirroring for repos with up to 10 Git and SVN users. It also has time-trial version that will mirror repo with any amount of users for one month. If you’re daring enough, you can also use EAP or interim builds. Note that it seems that interim builds don’t have any time/user limits whatsoever.

With SubGit, I was able to convert abovementioned SVN repo to Git overnight without any extra steps, using this simple command:

subgit import --svn-url http://server/svn/my/nested/repo --authors-file .\authors.txt .\repo.git

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Migrating a SVN repo to Git: a tale of hacking my way through

  1. ➤ Migrating a SVN repo to Git: a tale of hacking my way through
  2. Migrating a SVN repo to Git, part deux: SubGit to the rescue

If you’re just looking for an easy way to do SVN-Git migration, skip this post and go directly to the part two instead.

We become what we behold. We shape our tools, and thereafter our tools shape us.
― Marshall McLuhan

Lately I’ve orchestrated a SVN to Visual Studio Online migration for one of our projects. Our developers opted to use a Git as version control solution, instead of Team Foundation Version Control (TFVC). Also, we have a pure Windows environment, running VisualSVN Server, so I’ll provide Windows-specific tips along the way.

Git and SVN are quite different beasts, especially when it comes to access control and branching strategies. Because of that, simply using Git’s bidirectional bridge to Subversion called git svn will produce suboptimal results. You will end with all branches and tags as remote svn branches, whereas what you really want is git-native local branches and git tag objects.

To alleviate this issue, a number of solutions is available:

A tool for editing version-control repository history reposurgeon enables risky operations that version-control systems don’t want to let you do, such as editing past comments and metadata and removing commits. It works with any version control system that can export and import git fast-import streams, including git, hg, fossil, bzr, CVS, and RCS. It can also read Subversion dump files directly and can thus be used to script production of very high-quality conversions from Subversion to any supported DVCS.
Agito is (yet another) Subversion to Git conversion script.It is designed to do a better job of translating history than git-svn, which has some subtleties in the way it works that cause it to construct branch histories that are suboptimal in certain corner case scenarios.
svn2git is a tiny utility for migrating projects from Subversion to Git while keeping the trunk, branches and tags where they should be. It uses git-svn to clone an svn repository and does some clean-up to make sure branches and tags are imported in a meaningful way, and that the code checked into master ends up being what’s currently in your svn trunk rather than whichever svn branch your last commit was in.

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