TL;DR — Typeahead/Autocomplete

Design a typeahead/autocomplete system like Google Search suggestions. As a user types each character, the system returns the top 10 most relevant completions in under 100ms. The suggestions must update with every keystroke, so the system must handle extremely high query rates with ultra-low latency. Key features: Return top 10 suggestions for any prefix. Suggestions ranked by popularity, recency, and personalization.