Interview prep

System Design Interview Questions

System design rounds evaluate structured thinking: requirements, estimation, a workable design, then bottlenecks and trade-offs.

Questions and answers

01How do you start a system design interview?

Clarify functional and non-functional requirements, agree on scale estimates, then sketch the API before drawing any boxes. Jumping to architecture first is the most common failure.

02How do you scale reads on a relational database?

Caching, read replicas, denormalised read models and finally partitioning. Each step adds staleness or operational cost, so justify why the previous one ran out.

03When would you introduce a message queue?

To decouple producers from consumers, absorb bursts and make retries safe. It buys availability at the cost of eventual consistency and duplicate delivery handling.

04Explain the CAP theorem in practical terms.

During a network partition you choose consistency or availability. Most product systems pick availability with eventual consistency; payments and inventory usually pick consistency.

05How do you make a write endpoint idempotent?

Accept a client-supplied idempotency key, persist it with the result, and return the stored result on retry.

How to answer these well

Interviewers are not grading recall — they are checking whether you've hit the failure mode the question describes. Anchor every answer to something you actually shipped or debugged with System Design.

Say the trade-off out loud. "I'd use X here, but it costs Y under Z conditions" scores higher than a clean textbook definition every time.

Roles asking for System Design

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