Collaborative Editor (Google Docs)

How this problem is worked

Ten stages, from the questions you would ask an interviewer to the trade-offs you would defend. Each asks one question, and the simulator runs the architecture you draw against the requirements you wrote.

1. 01ClarificationsWhat would you ask before drawing a single box?
2. 02Functional reqsWhat must this system actually do?
3. 03Non-functionalWhat must it promise about speed, uptime and correctness?
4. 04Capacity estimationHow much load and data does this have to hold?
5. 05API designWhat does the outside world call, and what comes back?
6. 06Data modelWhat gets stored, and what is it looked up by?
7. 07Use-case breakdownHow does each requirement actually get served?
8. 08High-level designWhich components handle a request, and in what order?
9. 09Deep divesWhich part breaks first, and what do you do about it?
10. 10Trade-offsWhat did this design cost, and what breaks at 10×?

Primary sources for this problem

• Figma — How Figma's multiplayer technology works (Evan Wallace)
• Figma — Making multiplayer more reliable
• Figma — Live migration of multiplayer servers
• ProseMirror — Collaborative Editing (Marijn Haverbeke)
• Apache Wave — Operational Transformation paper (Wang et al.)
• Shapiro et al. — Conflict-free Replicated Data Types (CRDTs)
• Yjs — Awareness, YATA internals
• Notion — How we made Notion available offline
• Atlassian — Administering Confluence Synchrony
• Lamport — Time, Clocks, and the Ordering of Events
• AWS — Exponential Backoff and Jitter (Marc Brooker)
• Kafka KIP-405 — Tiered Storage