G19 · Design Google Docs Realtime Collaboration G19 · 设计 Google Docs 实时协作
Verified source经核实出处
Google Docs is canonical realtime collab; SD interview classic. Credibility A.
Key decisions关键决策
- **Operational Transformation** (Google's original) or **CRDT** (modern). OT needs server authoritative; CRDT allows P2P.**OT**（Google 原版） 或 **CRDT**（现代）。OT 需服务端权威；CRDT 可 P2P。
- **Per-document fan-out**: WebSocket session, server sequences ops, broadcasts to other clients.**按文档 fan-out**：WS 会话，服务端定序 op，再广播。
- **Offline queue**: local CRDT/OT state; reconcile on reconnect.**离线队列**：本地 CRDT/OT；重连时对齐。
- **History**: compressed op log; replay for timeline view.**历史**：压缩 op 日志；重放用于时间线。
Follow-ups追问
- Presence scale? heartbeat + short-TTL cache.在线状态规模？心跳 + 短 TTL 缓存。