Your question is PostgreSQL Isolation Levels for Payments. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
Transaction isolation matters whenever you read and update financial data concurrently, such as balances, card charges, or bank transfer states. In PostgreSQL, choosing the wrong isolation level can lead to inconsistent reads or unnecessary contention.
You are asked to explain PostgreSQL isolation levels and how they prevent anomalies such as dirty reads, non-repeatable reads, and phantom reads. Your answer should compare READ COMMITTED, REPEATABLE READ, and SERIALIZABLE, clarify what PostgreSQL does with READ UNCOMMITTED, and describe which anomalies are still possible at each level.
The interviewer expects a practical database answer rather than a purely textbook one. You should define each anomaly clearly, relate it to PostgreSQL's MVCC behavior, and mention the trade-off between stronger consistency and lower concurrency in systems that process card payments, bank transfers, or ledger updates.