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News Feed System Design
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Scenario
Election night: posts per second 10× normal and timelines lag 30 minutes unless you already planned hybrid fan-out and ranker timeouts. Users tolerate stale order more than an empty feed—the interview mirrors Facebook/Twitter feed mechanics with ranking called out.
Design a news feed where users publish posts and followers see a ranked or chronological timeline. This is the classic fan-out on write vs read problem with celebrity exceptions and ranking latency budgets.
You should support post creation, follow graph, home feed pagination, reactions, and ranking. Be ready to explain hybrid fan-out, degradation, and cursor pagination.
Constraints
Create post, follow graph, home feed, like/comment, rank or chronological mode, pagination
< 300 ms feed p95, high availability, seconds staleness on rank OK
1B users, 500M DAU, hundreds of millions posts/day, reads >> writes
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