System designHardsd-g267

Subject Fan outLevel Senior–Staff~50 minCommon in Distributed systems interviewsIndustries Technology

Question

Design a market-data fan-out system that distributes live price ticks for 100,000 instruments to 500,000 subscribers (web, mobile, and pro terminals). Updates arrive at up to 2M ticks/sec from exchanges; web clients want <250 ms freshness while pro terminals demand <5 ms. Many instruments are quiet while a few (e.g., a hot crypto pair on a volatile day) carry 90% of the volume. How do you fan this out without overwhelming clients or the network?

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.