Start by clarifying requirements and scale, then propose a high-level architecture with idempotency and distributed transactions as core components. Dive into critical flows like payment processing and provider integration, emphasizing trade-offs and failure handling.
Pro tip: Focus on idempotency and exactly-once semantics early, as they are the hardest parts of payment systems. Also, discuss how you would monitor and reconcile transactions to detect and resolve double charges.
Ask questions to understand expected throughput, latency, consistency needs, payment methods, and provider integration details. Confirm the scale of tens of thousands of TPS and any regional or regulatory constraints.
Sketch a scalable, fault-tolerant architecture with load balancers, stateless services, message queues, and databases. Include components for idempotency, transaction logging, and provider adapters.
Detail the steps from receiving a payment request to final settlement, ensuring idempotency via unique keys and distributed transactions (e.g., saga pattern). Explain how to handle provider callbacks and timeouts.
Discuss partitioning, sharding, caching, and asynchronous processing to handle high TPS. Cover retries, circuit breakers, and dead-letter queues for resilience.
Explain mechanisms like idempotency keys, exactly-once processing, and reconciliation jobs. Describe how to detect and resolve duplicates, and how to handle provider-side idempotency.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.