Real-time engagement features
Design the real-time *engagement-feature* pipeline that feeds a search ranker: the ranker uses features like 'this item's click-through rate over the last 1 hour / 24 hours / 7 days' and 'this item's add-to-cart rate today', and these counters must update within seconds of user events so a suddenly-popular item ranks up quickly. You have millions of items and 200k engagement events/sec. How do you compute and serve these time-windowed counters at low latency, and how do you keep them from being gamed or skewed by a single burst?
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 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.