System designHardsd-g507

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

Question

Design a delayed/scheduled message service that lets producers enqueue a message to be delivered at an arbitrary future timestamp (from seconds to 1 year out). Scale: 500M scheduled messages in flight, 50K new schedules/sec, delivery accuracy within ±1s of the target time, at-least-once delivery to downstream consumers. Schedules can be cancelled or rescheduled before they fire.

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.