Spent way too long on the API and DB layers and basically ran out of runway before getting to the file generation piece, which was clearly the whole point.
Start by clarifying requirements and scale, then design the data model and state machine for purchase requests and approvals. Describe the batch settlement process, focusing on reliability, idempotency, and performance. Discuss trade-offs and potential bottlenecks.
Pro tip: Emphasize idempotency and exactly-once processing in the batch job, as payment systems must handle retries and failures gracefully. Also, consider using a distributed lock or leader election to ensure only one settlement job runs at midnight.
Ask about scale (transactions per day, peak load), consistency requirements, and failure handling. Understand the approval workflow and settlement file format.
Define entities: PurchaseRequest, Approval, Transaction, SettlementBatch. Choose a database (SQL for ACID) and design schemas with appropriate indexes.
Outline REST endpoints for creating requests, approving/rejecting, and querying status. Define state transitions (e.g., PENDING, APPROVED, REJECTED, SETTLED).
Describe how to generate the settlement file at midnight: query all approved transactions from the day, format them, and write to a file (e.g., CSV). Ensure idempotency and handle failures with retries.
Discuss partitioning, read replicas, asynchronous processing, and monitoring. Consider using a job scheduler (e.g., cron) and a distributed lock to prevent duplicate runs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.