Capacity Planning

Build the suggestion service behind a search box. As a user types a prefix, the service returns the top few completions of that prefix, ranked by how popular each completion is. A user typing car should see cardigan, car rental, cards — the most-searched continuations, not a random match.

In scope: returning the top-K completions of a prefix, ranking them by popularity, and ingesting the search and click signals that popularity is built from. Out of scope: the full search results page, the search engine that answers the chosen query, spell correction, and per-user personalization. Those last two return as variants at the end.

K and top-K. K is the size of the suggestion list — usually 5 to 10. "Top-K" means the K highest-ranked completions of a prefix, e.g. the 10 most-searched queries that start with car.