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.