Capacity Planning
Design Live Comments (Real-Time Fan-Out) · Part 5
Problem context
Design live comments on a live broadcast: viewers type short comments, and every viewer watching sees new comments stream in near-real-time.
In scope: posting a comment on a broadcast, broadcasting new comments to every connected viewer in near-real-time, and delivering a readable stream even when comments arrive faster than anyone can read. Out of scope: long-term comment history and search, machine-learning moderation, and the live video stream itself.
What a strong answer sounds like
State the decision, connect it to a requirement, and name the tradeoff. Keep the design focused on the workload in the prompt.
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