Collaborative document concurrency
Design the concurrency control for a collaborative document store where many users edit the same record/document and you must reconcile concurrent writes without a global write lock. Use optimistic concurrency control (OCC). Constraints: ~10k concurrent editors across thousands of docs, writes must not silently overwrite each other (lost-update protection), and the common case (no conflict) should be lock-free and fast. Describe the storage/versioning, how concurrent writers detect conflicts, and what happens on a conflict.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.