Design Typeahead

1. Problem Statement

2. Architecture Discussion Map

Use this as one discussion aid, not a single correct answer. Your design should follow from the requirements, scale, and trade-offs you establish.

graph LR
    A["Design Typeahead"]
    A --> F1["Prefix index and top-K precomputation"]
    A --> F2["Index memory sizing and pruning"]
    A --> F3["Caching at client, edge, and server"]
    A --> F4["Offline builds, freshness, and atomic index swaps"]
    A --> F5["Safety filtering, blocklists, and privacy thresholds"]

3. Key Focus Areas

• 1
  Prefix index and top-K precomputation
• 2
  Index memory sizing and pruning
• 3
  Caching at client, edge, and server
• 4
  Offline builds, freshness, and atomic index swaps
• 5
  Safety filtering, blocklists, and privacy thresholds

4. What the Interviewer Looks For

The interviewer probes these areas, and the report grades the interview against them.

• Requirements and estimation
• Prefix-serving structure
• Data pipeline and freshness
• Caching and client request control
• Ranking quality, safety, and operations

5. What Strong Candidates Should Demonstrate

• Size a prefix index from query counts and decide what to prune or shard.
• Serve precomputed top completions per prefix within a tight latency budget.
• Cache shared suggestions in the browser, at the edge, and on servers.
• Keep suggestions fresh, and keep harmful or private queries out of them.