A snapshot is a complete representation of a model at a specific moment in its commit history. A branch is a mutable named reference to a specific commit. A ‘lock’ is an immutable, user-defined named reference to a specific commit. Branches and locks both act as references to commits, so collectively they are called ‘refs’.
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MMS5 uses refs to track which commits should have snapshots. Branches are mutable refs that automatically get adjusted to point at the latest commit when an update is made. Locks are immutable refs that can only be created and destroyed. Users can create namespaced locks in order to ‘lock’ access to a particular commit’s data (via its corresponding snapshot), and then subsequently delete locks to ‘release’ access.
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