Didn't get all the test cases to pass, which had me pretty sure I was done.
Start by clarifying the functional and non-functional requirements, such as supported operations (deposit, withdraw, transfer), consistency guarantees, and scale. Then design a layered architecture with a transactional core (e.g., using ACID-compliant database) and discuss how to handle concurrency, idempotency, and fault tolerance. Finally, walk through the data model, API design, and trade-offs for scaling and reliability.
Pro tip: Emphasize idempotency and exactly-once processing for financial transactions, and mention how you would handle race conditions with optimistic locking or serializable isolation. Also, proactively discuss monitoring and audit trails, as these are critical in banking systems.
Ask questions to understand the scope: what operations are needed (e.g., create account, deposit, withdraw, transfer), expected throughput, consistency requirements, and any regulatory constraints.
Define entities like Account, Transaction, and Ledger. Choose a relational database for ACID guarantees, and design schemas with proper indexes and constraints.
Discuss techniques to prevent race conditions and ensure data integrity, such as pessimistic/optimistic locking, serializable isolation levels, or distributed transactions if scaling out.
Address fault tolerance with replication, sharding, and idempotent APIs. Consider using message queues for asynchronous processing and event sourcing for auditability.
Summarize key trade-offs (e.g., consistency vs. availability, latency vs. durability) and suggest potential improvements like caching, read replicas, or microservices decomposition.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.