Netflix·Software Engineer·Onsite - System Design / Architecture
May 2026
Netflix system design round for a software engineer role, focused entirely on building a thread-safe in-memory key-value store for a multi-threaded AI platform. The question had a lot of sub-parts and went pretty deep into concurrency, testing, and production concerns.
- What internal data structure would you use to back a thread-safe key-value store, and why?
- Walk through different synchronization strategies for a shared key-value store: single global lock, per-key locks, lock striping, or a built-in concurrent map. What are the trade-offs?
- Implement put, get, and delete for a thread-safe key-value store in Python, which has no built-in concurrent map.
- How would you test a concurrent key-value store for correctness and race conditions? Think unit tests, stress tests, and any tooling.
- If this key-value store were used in production, what additional concerns would you address beyond basic correctness?
“Started with a plain hash map and explained why, which felt almost too obvious.” The rest of the author's notes on Software Engineer interview at Netflix, Onsite - System Design / Architecture round, covers how they worked through the question, what the panel pushed back on, and what they would do differently.
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