System design interview question
Design a Real-time Collaborative Document Editor with Conflict Resolution (like Google Docs)
Design a distributed system for a real-time collaborative document editor supporting 500M users with 5M concurrent active editors. The system must handle simultaneous edits from multiple users on the same document with sub-second propagation latency, automatic conflict resolution using operational transformation or CRDT, persistent storage with full audit trails, and offline-first capabilities with eventual consistency guarantees. Documents range from 10KB to 100MB, with peak write throughput of 50K operations/second across all documents. The system must be globally distributed across 3 continents with 99.99% availability SLA and support for real-time presence awareness. Design the architecture considering network partitions, stale reads, and the complexities of merging concurrent non-commutative operations while maintaining causal consistency.
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