Tell about your experience working with financial/transactional services.

In working with financial and transactional services, key aspects include:

• Ensuring atomicity and consistency of transactions. Using ACID transactions in databases so that operations are either fully completed or rolled back.
• Error handling and rollbacks. It is important to handle failures correctly to prevent partial changes.
• High availability and fault tolerance. Financial services must operate without downtime.
• Data security. Encryption, access control, auditing.
• Performance and scalability. Query optimization, caching, using queues for asynchronous processing.

For example, when implementing a payment service, I used database transactions for debiting and crediting funds to avoid balance desynchronization. I also implemented retry and compensation mechanisms in case of failures.