How to transform a project from a huge subversion repository to git
Published: 2014-05-06

Disclaimer: I’ve written this post a while ago and I am not entirely sure how accurate it was the time I stopped proof-reading it. So take with care and always keep a backup. The information provided here might be outdated, or even wrong. I hope, it still helps someone getting rid of overly large SVN-repositories.

Multi-project subversion repositories sound convenient at the first glance: Everything at one place and only one system to manage. If you ever consider to switch over to git it is a bad idea. Usually transforming a subversion into a git repository is quite easy, but that is only valid for repositories of a reasonable size. Multi-project repository tend to grow quite big. The usual transformation via git svn clone <svn-url> extremely slows down on huge repositories. I once had to convert some projects from a SVN-repository with at the end 141 more or less active projects and around 470000 commits…

A short overview of what is required

• Time. It doesn’t take weeks anymore, but it still requires some time (I got it working in around 4 hours at the end, but after I had created a local repository)
• A fast storage. The whole process is extremely IO-intensive. A SSD works fine, even better — if there is enough RAM available — is a RAM-disk of around 4 to 8 GB.
• svnrdump. This is part of SVN 1.7.
• I used svn-all-fast-export for the actual conversion (it’s available in the ubuntu repository). svn-fast-export should work too, but I had issues with that and stopped investigating.
• BFG Repo-Cleaner to get rid of large files and files containing sensitive data.
• Of course Subversion (especially svnadmin) and git.

# Step 1: Create a local copy

If you already have access via filesystem to the repository you can skip this step. This is to create a local copy of a remote repository, so that we don’t have to perform every operation over the network.

# First one without "--incremental"
svnrdump dump \
--revision 0:10000 \
http://example.com/path/to/svn/MyProject | gzip -9 > MyProject.00.svn.gz
for i in {01..39}; do
svnrdump dump \
--incremental \
--revision $(($i))0001:$(($i+1))0000 \
http://example.com/path/to/svn/MyProject | gzip -9 > MyProject.$i.svn.gz done; # Create local repository and import the chunks mkdir MyProject.svn sudo mount -t tmpfs none MyProject.svn # Skip this, if you don't want to use a ramdisk, # but you have to deal with the consequences yourself svnadmin create MyProject.svn for i in {00..39}; do gunzip < MyProject.$i.svn.gz | svnadmin load --quiet --force-uuid MyProject.svn;
done;

svnadmin dump --quiet MyProject.svn | gzip -9 > MyProject.svn/MyProject.svn.gz

mv MyProject.svn/MyProject.svn.gz /path/to/backup/


The import of the full-backup into a ramdisk-SVN-repository is quite fast (took me around 5min), so it’s fine to just keep this and rebuild the repo a new after a restart.

# Step 2: Prepare export

SVN tracks committers only by an username, but git by an email-address with an additional, optional and arbirtrary (display-)name. Create a script, paste the following code into it and make it executable. Note, that you must change the path to your local SVN-repository.

#!/usr/bin/env bash
authors=$(svn log -q file:///absolute/path/to/MyProject.svn | grep -e '^r' | awk 'BEGIN { FS = "|" } ; { print$2 }' | sort | uniq)
for author in ${authors}; do echo "${author} = ${author} <${author}@example.com>";
done

./extract-authors.sh > authors.txt


Fix the content. git-all-fast-export (and as far as I know all the other tools too), expect a format svn-user-name = committer name <[email protected]>. It’s really easy. If you don’t know each and every name, it doesn’t matter.

# Step 3: Export

The ugliest part is creating the “rules”-file. svn-all-fast-export expects a rules file, that contains rules on how to map paths in SVN to git branches and tags. For further options, see Gitorius samples

create repository MyProject
end repository

match /MyProject/trunk/
repository MyProject
branch master
end match

match /MyProject/branches/([^/]+)/
repository MyProject
branch \1
end match

match /MyProject/tags/([^/]+)/
repository MyProject
branch tag/\1
end match

match /MyProject/tags/([^/]+)/
repository MyProject
branch refs/tags/\1
end match

match /
# ignore everything we don't know (remove/comment this to find missing mappings)
end match


As you can see every mapping is prefixed with “MyProject”, because this tool isn’t able to strip the project path itself.

svn-all-fast-export --identity-map=authors.txt --rules=my-rules.rules /path/to/local/svn


If everything worked fine, you know should have the bare git repository in a subfolder named MyProject. Theoretically you are finished now.

# Step 4: Cleanup

First we simply drop all already merged branches. If they are already merged, you don’t need them anymore and you can re-create the branch, when you need it again.

git branch -d git branch --merged


[BFG here]

git reflog expire --expire=now
git gc --aggressive --prune=now


One thing, that is a little bit annoying is, that for whatever reason svn-all-fast-export exports the svn:ignore property into an .svnignore file. With some git “black magic” you can rename the file in the whole repository. I recommend it as the last step, because it is by far the most time consuming step when handling with the git repository, but it is at least faster, when the repository is already smaller.

git filter-branch --index-filter 'git ls-files -s \
| sed "s-$\t\"*$.svnignore-\1.gitignore-" \
| GIT_INDEX_FILE=$GIT_INDEX_FILE.new git update-index --index-info && mv "$GIT_INDEX_FILE.new" "\$GIT_INDEX_FILE"' HEAD


However, this isn’t completely sufficient. svn-all-fast-export doesn’t convert svn:ignore-properties in subfolders. A good start to fix this manually (at least in the master-branch) is svn propget -R and compare it with the .gitignore. Also it is a good idea to review, if it really covers everything, that should get ignored. I wouldn’t spend too much time into this, because it only affects developing and it only affects “living” branches.