System design interview question
Design a Real-time Collaborative Document Editor with Conflict Resolution (like Google Docs at Scale)
Design a distributed system that powers a real-time collaborative document editing platform supporting 500M monthly active users with 50M concurrent editors at peak. Users across multiple geographic regions must see sub-500ms latency for edits, with strong eventual consistency guarantees and no lost updates. The system must handle 1M concurrent document sessions, each with 2-10 simultaneous editors, persisting documents to durable storage while maintaining full edit history and undo/redo capabilities. Key constraints: support offline editing with conflict resolution on reconnect, handle network partitions gracefully, provide rollback capabilities for concurrent edits, and scale horizontally across regions without a single point of failure.
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