Design a Real-Time Suggestions Service

Q: Design a Real-Time Suggestions Service

This is a System Design interview question from SoFi for Software Engineer roles. View the full question and solution on PracHub.

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Question

System Design: Real-Time Typeahead/Autocomplete

Context

Design a real-time typeahead/autocomplete service for a consumer-facing web and mobile application. Users see suggestion updates on each keystroke. Assume global traffic, multiple locales, and both anonymous and signed-in users.

Requirements

Design the system and cover:

API design and request/response schemas
Data modeling and indexing (e.g., prefix trees, FST, inverted indexes)
Ranking signals and personalization
Latency targets and budgets (e.g., P95 < 100 ms)
Caching layers (edge, in-memory, distributed)
Scalability and capacity planning
Freshness and backfill pipelines (batch + streaming)
A/B experimentation hooks and telemetry
Failure handling and graceful degradation

State assumptions where needed and justify trade-offs.

Design a Real-Time Suggestions Service

System Design: Real-Time Typeahead/Autocomplete

Context

Requirements

Solution (Locked)

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