System Design: The Typeahead Suggestion System

Design a service that returns useful completions while a person is still typing. Its serving path must be fast, but the data used to rank suggestions can often be prepared separately. This chapter follows that separation from workload estimates to index updates.

Introduction

A Typeahead suggestion (or autocomplete) system provides real-time query suggestions as users type. It helps users quickly locate common or previously searched terms. The system generates ranked suggestions based on search history, current context, and trending queries. Although typeahead does not improve the execution speed of the search query, it reduces the time needed to formulate a query. Ranking algorithms determine the relevance and order of these suggestions.

Common applications include: