Design a Collaborative Editing System (Google Docs)

To design a Google Docs-like system, I would start by defining the core requirement: low-latency synchronization across thousands of concurrent users with eventual consistency. The architecture would feature clients connected via WebSockets to a gateway, which routes commands to a state management service. For the critical merge logic, I recommend using CRDTs (Conflict-Free Replicated Data Types) over traditional Operational Transformation. CRDTs allow independent updates to be applied locally first and merged later without needing a central lock, which drastically reduces server load and handles network partitions gracefully. Specifically, I would implement a RGA (Replicated Growable Array) for text editing, where each character is an object with a unique ID. When two users insert text at the same index simultaneously, their unique IDs determine the final order mathematically, ensuring convergence without complex transformation logic. The server acts as a broadcast hub, validating operation syntax but not enforcing strict ordering on every request. For heavy loads, we could shard documents by ID. If we chose OT instead, we would need a central sequencer to timestamp operations and transform incoming changes against the current document state, which introduces a single point of contention. Given Google's focus on scalability and resilience, the CRDT approach offers superior fault tolerance and allows clients to remain responsive even during brief connectivity issues.