Your question is URL Shortener Concurrency. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Design a URL shortener that deletes old URLs and works in a multiprocessor environment with concurrent reads and writes.
Asked in the round 3 stage.
Explain the practical design, including URL creation, lookup, expiration, deletion, synchronization between processes, storage choices, and behavior during failures. Address how you would prevent stale reads, lost updates, duplicate short keys, and races between deletion and lookup.