System designHardsd-g069

Subject RecommendationLevel Senior–Staff~55 minCommon in ML systems interviewsIndustries Technology, Software development

Question

Design the home-page recommendation system for a podcast app with 100M users and 5M shows (50M episodes). The home feed must mix continue-listening, new-episode alerts from followed shows, and discovery. Constraint: p95 under 200ms for the full feed, the catalog has heavy popularity skew, and episodes go stale fast (a daily news show episode is worthless in 48h).

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.