Explain sync/async, Go concurrency, SQL vs NoSQL

You are interviewing for a backend engineering role. Answer the following conceptual questions clearly and with concrete examples.

1) Synchronous vs asynchronous

• Define synchronous and asynchronous execution.
• Explain how this differs from blocking vs non-blocking I/O.
• Give an example of each in a backend service (e.g., handling HTTP requests, calling downstream services).

2) Go: channels vs shared-memory concurrency

• Explain Go’s concurrency model at a high level (goroutines, scheduler).
• Compare communicating via channels vs sharing memory with locks .
• When would you prefer each approach? Call out common pitfalls (deadlocks, data races, goroutine leaks).

3) SQL vs NoSQL

• Compare relational databases and common NoSQL types (key-value, document, wide-column).
• Discuss trade-offs across:
  • data modeling and query patterns
  • transactions and consistency guarantees
  • scaling (vertical vs horizontal)
  • operational complexity
• Provide a couple of example use cases where you would strongly prefer SQL, and where you would strongly prefer NoSQL.