System designHardsd-g337

Subject RankingLevel Senior–Staff~50 minCommon in ML systems interviewsIndustries Technology

Question

Design the ranking layer for a feed that must optimize *multiple competing objectives at once*: predicted click, predicted long-dwell, predicted 'meaningful interaction' (comment/share), and a penalty for low-quality/clickbait. Each is a separate model producing a probability; the final order must combine them into one score. Product keeps wanting to retune the balance (push 'meaningful interactions' up before an election; push dwell up to grow watch time) without a code deploy. Design the scoring and the tuning mechanism.

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.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.