Tony has provided the following feedback on your session:
Sida demonstrated strong clarity and initiative in breaking down the system design for a payment platform. The session covered key aspects including requirements, API design, high-level components, and scalability strategies.
Areas of strength included:
- Quickly enumerated core functional and non-functional requirements
- Clearly identified key entities and drew distinctions between Payment and Transaction
- Completed a comprehensive API definition and began expanding entity schemas
- Initiated a meaningful deep dive into security topics, including tokenization strategies like iframe usage
- Considered idempotency with a composite deduplication key strategy
- Discussed scalability with merchant-based sharding and CDC-based state syncing
Areas for improvement:
- Include payment settlement as a distinct functional requirement early on
- Tie quantitative metrics (e.g., latency, throughput, durability goals) to each non-functional requirement
- Clarify durability guarantees (e.g., traceability of failed transactions, state recovery post-crash)
- Include more details in API responses, such as status and timestamps
- Embrace more collaborative moments with your interviewer—for instance, naturally inferring steps like DB validation during payment creation
- Security discussion could go deeper—mention options but also evaluate tradeoffs (e.g., why iframe vs vault? what about field-level encryption?)
- Demonstrated some hesitation around data correctness guarantees — aim to confidently frame how at-least-once delivery + deduplication = exactly-once semantics
- Current scalability thinking ends with DB writes—consider decoupling with messaging queues to prevent bottlenecks
Overall, Sida shows great structure and promise in system design interviews. With additional work on durability, correctness, and deeper tradeoff thinking (especially in Staff+ topics like encryption, failure modes, and collaboration signals), they’ll be well-positioned for success in senior-level interviews.