Automatically synchronizing a Subversion repository and a Git repository

Question

My project has a Subversion repository on a network file system, and a new team would like to access it using Git, and be able to commit to it and get updates from it.

What I have in mind is to create a new bare git-svn clone of the Subversion repository on the same network file system, and make sure the two repositories are always up to date with respect to each other.

The way to do this is probably to add a post-commit hook for both Subversion and the new Git repository, that will each update the other's repository.

The Subversion post-commit hook will include git svn rebase, and the Git one git svn dcommit.

The problem is that I will have to use some kind of lock to make sure no one commits to either repository while other is also being committed to, because they always have to be in sync before any commit. This has several disadvantages, among them the time it will take to commit to Subversion or to push to the Git repository (it has to wait for the hook to finish), and the fact that some users may not be able to run git svn (because it's not installed on their machine), which means they can't update the other repository when committing/pushing.

How can I solve these problems? What will the Subversion and Git hooks look like?

Daniel Hershcovich Daniel Hershcovich · Accepted Answer · 2011-10-04T08:58:53

Here is what I've come up with:

Create the git-svn repository if it doesn't exist already:
```
git svn init --std-layout <svn_url> <git-svn_path>
```
The master branch is created automatically to track the trunk.

To avoid name ambiguities with Subversion-tracking branches, make the original Subversion branches show as remotes/svn/<branch name>: go to the newly-created git-svn repository and run

git config svn-remote.svn.fetch trunk:refs/remotes/svn/trunk
git config svn-remote.svn.branches branches/*:refs/remotes/svn/*
git config svn-remote.svn.tags tags/*:refs/remotes/svn/tags/*

rm .git/refs/remotes/*
git svn fetch

Create a Subversion-tracking branch for each Subversion branch:

for BRANCH in $(svn ls <svn_url>/branches/); do
    git branch $BRANCH remotes/svn/$BRANCH
done

Make sure no non-Subversion-tracking branches are created on the central Git repository:

# Used by hooks/update:
git config hooks.denyCreateBranch true
git config hooks.allowDeleteBranch false

cp .git/hooks/update.sample .git/hooks/update
chmod +x .git/hooks/update

Allow pushing to the central Git repository:

git config receive.denyCurrentBranch ignore
git config receive.denyNonFastForwards true
git config push.default current

And create the post-receive hook to reset and send the commits to Subversion:

cat .git/hooks/post-receive

    #!/bin/sh

    date >> receive.log
    git reset --quiet --hard
    while read LINE
    do
        BRANCH=${LINE##*/}
        echo Updating $BRANCH
        git checkout --quiet --force $BRANCH
        git svn dcommit
    done 2>&1 | tee -a receive.log
    git checkout --quiet --force master

chmod +x .git/hooks/post-receive

The reset is necessary, because otherwise the current branch is out-of-date after each receive.

Finally, create the hook to get updates from Subversion:

cat .git/hooks/svn-rebase-all

    #!/bin/sh

    date >> .git/svn-rebase.log
    git reset --quiet --hard
    for REF in .git/refs/heads/*
    do
        BRANCH=${REF##*/}
        echo Updating $BRANCH
        git checkout --quiet --force $BRANCH
        git svn rebase
    done 2>&1 | tee -a .git/svn-rebase.log
    git checkout --quiet --force master

chmod +x .git/hooks/svn-rebase-all

And call it from the Subversion post-commit hook:

cat <svn_path>/hooks/post-commit

    cd <git_path>
    . .git/hooks/svn-rebase-all

chmod +x <svn_path>/hooks/post-commit

Instead of using a single git-svn central repository, one can use a bare central Git repository and an intermediate non-bare git-svn repository, as in this answer. I chose to use one non-bare git-svn repository which is also the central repository.

Anyone can work on the project using Git by cloning <git_path> and pushing to it, or using Subversion by checking out <svn_url> and committing to it.

Automatically synchronizing a Subversion repository and a Git repository

2 Answers