Design a social media news feed system (like Facebook or Twitter). Users follow other users and see a feed of recent posts from people they follow, ranked by relevance. The system should support 100 million users with an average of 200 follows each.
Cover: feed generation, ranking, storage, caching, and the fan-out strategy.
How to approach it
- Hint 1
The core tradeoff is fan-out on write (push model) vs. fan-out on read (pull model).
- Hint 2
Celebrity users with millions of followers make pure fan-out on write expensive.
- Hint 3
A hybrid approach handles normal users and celebrities differently.
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