System designHardsd-g096

Subject Ab testing mlLevel Senior–Staff~40 minCommon in ML systems interviewsIndustries Technology, Software development

Question

Design the experimentation platform a search team uses to safely roll out new ranking models. They ship a new ranker every week, and a bad ranker hurts revenue and user trust immediately. You need to (a) detect within hours whether a new ranker is better or worse than the current one, (b) protect against a catastrophically bad model reaching all users, and (c) handle the fact that ranking quality is hard to measure with a single conversion metric. Design the rollout + evaluation system.

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.