Changing SVN Servers

I recently helped a team to switch SVN servers and found a few gotchas along the way. This is a short guide on what worked for me and some stuff I tried that didn’t.

The reason for migrating to a new subversion server was that Atlassian shut down their hosted subversion service. The team had been dragging out on the migration for far too long (there was more than a year’s notice). When they asked me for help, there were only a few days left before the old service was shut down. They said that they had considered moving to git and that there was probably a server set up somewhere by the operations department.

I had a quick look at the repo and asked the team about their situation and found out a number of facts to take in consideration for a move.

  • A gziped dump of the repo was about 1.3GB
  • The repo had not followed the standard trunk/branches/tag structure. A few levels below a trunk directory I found another set of directories: trunk, branches, tags.
  • The repo contained code from different projects. Some legacy that were no longer needed, some being actively developed.
  • There was no time for a long service window. I basically had to get everything moved from one working day to another.

.

Switching Servers

Based on those facts I first tried to use svnsync to make a new copy of the repo, while keeping the old one alive. It got stuck after a few hundred commits and then claimed the sync was broken. I reset the target repo and tried again, with the same result.

I gave up on using svnsync and reverted to the basic plan: download a backup and import to a repo on the target server. That worked.

These are the steps I did run to move the repo. Please note that the svnadmin commands need to be run on the source and destination servers. They cannot be run from a client.

  1. Dump the repo on the old server: svnadmin dump source | gzip > dump.gz
  2. Copy the dump file to the new server
  3. Create a new empty repo on the new server: svnadmin create dest
  4. Import the dump file to the new repo: gunzip -c dump.gz |svnadmin load dest

One thing that really surprised me was the size of the dump file vs the size of the repo. When I did this, I downloaded a .gz dump file. I didn’t create it myself, so I didn’t know how big the source repo was. What I knew was that the dump file was 1.3GB. Uncompressing it on my local computer gave 5GB and I only had about 5.5GB left on the destination server… However it worked out just fine: The final repo was just about 600 MB in size.

The reason for this is that the dump file contains a lot of duplicate information. When branching, the repo only contains a pointer back to the original commit, but the dump file contains the entire contents of the branch.

Avoiding git

For some people, “git” is the answer to any question about source control. In this case there were of course some people arguing for a move to git. While I really do like git, this wasn’t the right time for it. (I was thinking about writing “love git” but that would be wrong. I may like or dislike tools, but they are just tools and I try hard to not get so attached to a tool that I love it and start seeing it as the ONLY TRUE ANSWER)

The reasons that I didn’t recommend git was.

  • The team was not ready. Nobody on the team had git experience and they didn’t have enough understanding of how different git is in some ways.
  • The source repo was quite messy. It was not possible to make a clean import to git with git-svn.
  • The source repo was far too large to import into a single git repo. It contained things like build outputs that should not be imported into a new rpo.
  • Subversion is good enough for the needs of the team and it is less complex than git.
  • Albin Sunnanbo on 2013-10-31

    If you’re not on a dead old SVN (created with SVN <1.2) with Berkley DB or have upgraded your repository to FSFS you can just copy the repository from the file system instead of fiddeling with svnadmin dump.
    There is also an additional benefit to this: since the files in the repository never changes you can copy all existing files in repo/db/revs/ and repo/db/revprops/ in advance from a running repository and at the switch over point just sync a few additional revisions.
    This reduces the required service window.

    Don't forget to communicate how and when to use svn relocate to your users.

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Software Development is a Job – Coding is a Passion

I'm Anders Abel, a systems architect and developer working for Kentor in Stockholm, Sweden.

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