This was the main question and I got through it but the third part tripped me up.
Start by clarifying requirements: what operations are needed (deposit, withdraw, transfer), consistency guarantees, and scale. Then design a data model with accounts and transactions, ensuring atomicity and idempotency. Finally, discuss implementation details like locking, error handling, and how to handle concurrency.
Pro tip: Emphasize idempotency and exactly-once processing for transactions, as this is critical in financial systems to prevent duplicate charges. Also, mention the importance of audit trails and reconciliation.
Ask about expected operations, consistency requirements (e.g., ACID), scale (transactions per second), and failure scenarios. Confirm whether this is a single-account or multi-account system.
Define entities: Account (id, balance, currency, version) and Transaction (id, from, to, amount, status, timestamp). Consider using a ledger-based approach where balance is derived from transactions for auditability.
Use database transactions with appropriate isolation levels (e.g., serializable) or optimistic locking with version numbers. For distributed systems, consider two-phase commit or saga patterns.
Assign unique transaction IDs and store them to detect duplicates. Handle failures gracefully with retries and compensating actions. Ensure that partial failures do not leave inconsistent state.
Talk about partitioning accounts, using queues for asynchronous processing, and monitoring for anomalies. Mention the need for reconciliation and audit logs.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.