Mastering the Senior C# Engineer Interview

This page gathers more than 30 senior-level interview questions for a C# engineer, framed around financial systems and real-world scenarios. It focuses on transaction handling, distributed systems, performance, security, system design, and production concerns.

Reading notes

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• It proposes assessing practical experience with real C# senior engineering scenarios.
• It brings together questions and answers about transaction failures, deadlocks, concurrency, security, logging, APIs, and system design.
• For transaction failures, it recommends retry with idempotency, a retry policy with Polly, a background job queue, and database tracing.
• For deadlocks in SQL transactions, it suggests a consistent order of operations, reducing the lock scope, and retrying in case of deadlock.
• For high-volume concurrency, the text addresses the problem in the context of transactions and payments.
• To avoid double-spending in distributed transactions, the text includes a dedicated section on the topic.
• For real-time queries, it recommends database indexing and pagination in large queries.
• For API requests and authentication, there is a specific section on call security and authentication.
• For long-running processes in .NET, the text presents its own approach for this type of task.
• For race conditions in a multithreaded environment, it recommends database transactions with row-level locks.
• For logging and monitoring in production, there is a section focused on this topic.
• For API failures in a microservices architecture, the text dedicates a specific question.
• For concurrency in a banking system, there is a question focused on managing this scenario.
• For rate limit abuse, the text addresses preventing excessive API use.
• For data consistency between microservices, there is a specific section.
• For securely storing sensitive user data, the text proposes a dedicated approach.
• For real-time fraud detection, the text includes a question about this system.
• For memory leaks in long-running services, there is a specific question.
• For scalable logging, the text proposes a solution aimed at this goal.
• For time zones in a global financial system, the text addresses the topic directly.
• For scaling a .NET API to millions of requests, there is a dedicated question.
• For optimizing SQL in large-volume processing, the text brings another specific section.
• For large reports in a financial system, there is a question focused on this case.
• For eventual consistency in distributed systems, the text includes a separate question.
• For circuit breakers in microservices, there is a dedicated section.
• To prevent unauthorized transactions, the text addresses access control and security.
• For caching real-time banking data, the text presents a specific question.
• For securely storing API keys, there is a dedicated section.
• For WebSockets and SignalR in real-time updates, the text compares these paths.
• For massive fund transfers, there is a question about efficiency in this flow.
• For RBAC in a banking application, the text includes a specific section.
• For an event-driven architecture in banking notifications, the text brings its own question.
• For CQRS in a financial application, there is a section about separate read and write models.