System designHardsd-g037

Subject IndexingLevel Senior–Staff~45 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

Design the spatial indexing layer for a real-time driver-matching system: find the K nearest available drivers to a rider's location within a radius, in a city with up to 100k concurrently moving drivers each emitting a location update every 4 seconds, with p99 match-query latency under 50ms. Drivers' availability flips constantly. Describe the spatial index structure, how you handle the extreme update rate (every driver moves constantly), how nearest-K-within-radius queries run, and the central trade-off.

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.