G8 · Design Google Search Suggestions (Typeahead) G8 · 设计 Google 搜索建议（Typeahead）
Verified source经核实出处
Google typeahead is textbook SD question. Credibility A.
Key decisions关键决策
- **Trie with precomputed top-K per node** in RAM; O(prefix) lookup.**Trie + 每节点预计算 top-K**，RAM 内查找 O(prefix)。
- **Refresh tiers**: hour-level popular + minute-level trending + day-level long-tail.**刷新分级**：小时热门 + 分钟趋势 + 天级长尾。
- **Personalisation layer**: base + user re-rank (history, location).**个性化层**：基础 + 用户 re-rank（历史、位置）。
- **Safety filter** on suggestions.**安全过滤**。
Follow-ups追问
- Surface breaking news? streaming pipeline bumps trending bucket within 60 s.热点事件？流式管道 60 s 内更新 trending 桶。