System designHardsd-p003

Subject ScalabilityLevel Senior–Staff~45 minCommon in Distributed systems interviewsIndustries Technology, Software development

Question

Design a social media home feed (timeline) for 500M users. Compare fan-out-on-write versus fan-out-on-read and explain how you handle celebrity accounts with tens of millions of followers.

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.