G22 · Design Firebase Realtime Database / Pub-Sub G22 · 设计 Firebase 实时数据库 / Pub-Sub
Verified source经核实出处
Firebase is a Google product; interview question on data model + realtime delivery. Credibility A.
Key decisions关键决策
- **Hierarchical JSON document** with path-based subscriptions.**层次化 JSON 文档**，按路径订阅。
- **Tree-diff fanout**: writes compute diff, push to subscribers of affected paths.**树 diff fanout**：写入计算 diff，推送给受影响路径的订阅者。
- **Rules language** evaluated at server — auth + validation.**规则语言**在服务端求值——授权与校验。
- **Offline queue** on client; reconcile via diff merge.**客户端离线队列**；重连时 diff 合并。
Follow-ups追问
- Hot paths with millions of subscribers? hierarchical fan-out trees.热路径百万订阅？分层 fanout 树。