Best way to create an SVN-Mirror?

Hello all!

I am currently looking into the best way to set up an SVN mirror. I currently see three possibilities all with their own drawbacks:

• Have an SVN post-commit-Hook that is blocking and syncing via svnsync. The problem here is obviously, that the commit is blocking until the data is transfered to the mirror.
• Have an SVN post-commit-Hook that is non-blocking and syncing via svnsync. Here I see the following, more subtle problem: Imagine someone checks in a BIG file, and someone else shortly after that checks in a small file. Because the commit is non-blocking, two svnsync processes could be running at the same time and the small file could overtake the BIG file on the way to the mirror (this seems very time-critical and unlikely, although possible in principle). Their revision would swap.
• Sync like every fifteen minutes with a cron-job. Same problem if a commit takes longer than 15 minutes and obviously that time-delay.

Did I forget a possibility? Did I get something wrong? Any ideas? Thank you already!

Maybe I should note that the second possibility is the one suggested by different web-sites. E.g. see http://www.kirkdesigns.co.uk/mirror-svn-repository-svnsync

From serverfault roesslerj

• You could try an approach similar to the one we use at Atlassian

  http://blogs.atlassian.com/developer/2008/11/subversion_replication_at_atla.html

  disclaimer: I am currently an Atlassian employee, but was not involved in implementing this solution (only maintaining it)

  As I said above in the comment, svnsync, run from a remote repository behaves deterministically. It cannot apply changesets out of order. So the only problem you have using a remote repository is the amount of lag due to changeset propagation.

  Jim T : +1 for the observation that svnsync cannot get out of order, the only problem is the potential latency.

  roesslerj : You are totally right... I made a stupid thinking mistake. So the simple and beautiful SVN post-commit hook should do it in most cases. In case latency is a problem, one can take a look at the referenced Atlassian article. Thank you very much!

  Dave Cheney : Just be aware that the post commit hook will block the committer until the hook has run to completion. I'm not sure what happens if the post commit hook fails, I don't think the commit is rolled back, but it will be at least confusing.

  roesslerj : Well, using the post-commit hook, you can issue a command that immediately returns (e.g. via 'command &' on linux), having it non-blocking. Since the hook is post-commit it cannot rollback the commit. If svnsync fails, the next svnsync has to sync two revisions, which it simply does. The problem occurring here I would file under the topic latency.
  From Dave Cheney