System design interview question
Design a Global Real-Time Feed System like LinkedIn's Activity Feed
Design a distributed system that powers a real-time activity feed for 500M users across multiple regions, where users follow 1000s of other users and the system must serve personalized feeds with <500ms latency. The system ingests 2M write events per second (follows, likes, posts, comments) and must handle 50M concurrent reads during peak hours. Feed data must be eventually consistent within 5 seconds, support filtering/ranking by relevance, and gracefully degrade under regional failures. Consider how to optimize for both heavy follows (celebrity-like accounts with millions of followers) and typical user accounts, minimize storage costs for historical feed data, and support real-time notifications while maintaining data consistency across geographically distributed datacenters.
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