System designHardsd-g080

Subject News feedLevel Senior–Staff~55 minCommon in ML systems interviewsIndustries Technology

Question

Design the ML-ranked feed for a short-video app with 200M DAU where the feed is pure discovery (not follow-based) — every scroll picks the next best video from a 1B-video corpus. Optimize for watch-time and meaningful engagement, serve the next video in under 100ms, and incorporate integrity (don't over-amplify borderline/harmful content).

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.