Runnable that automatically publishes commits from storage to ZK.
Get the current version of some commit key.
Immutable, point-in-time view of all nonempty commits.
Live-updating view of all present commits.
Publish a new commit to ZooKeeper.
It's much more possible to prevent rollbacks when commit payloads are always nonempty. This is because empty commits are removed from ZooKeeper, which means we cannot distinguish them from commits that have simply never been published at all.