System designHardsd-g074

Subject PersonalizationLevel Senior–Staff~50 minCommon in ML systems · Distributed systems interviewsIndustries Technology

Question

Design a real-time personalization service that powers multiple surfaces (homepage modules, email, push) for a retail app with 300M users. It must blend long-term taste (built over months) with in-session intent (what the user clicked in the last 5 minutes), serve a personalized response in under 50ms, and let users reset/clear their personalization for privacy.

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.