Search Autocomplete
Suggest popular completions as users type, within tens of milliseconds.
Medium40 minTrieTop-KOffline aggregation
Search autocomplete (typeahead) suggests popular completions as the user types each character. It has a brutal latency budget, since a request fires on every keystroke, which pushes the design toward precomputed top-K results served from memory.
Clarify requirements
Functional
- Given a prefix, return the top 5–10 suggestions ranked mainly by popularity.
- Suggestions update as query trends change (daily is fine, near real-time for trending is a bonus).
- Filter offensive or blocked terms.
- Optional: personalization and locale; scope initially to global popularity per language.
Non-functional
- 100M DAU, ~10 searches each, ~6 keystrokes per search that trigger a request.
- p99 latency < 50 ms end to end (server time ~10 ms).
- Highly available; slightly stale suggestions are fine.
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