Backend interview questions are rarely about definitions. They’re scenarios: a retry charges a customer twice, two people buy the last item, a job crashes at record 7,000. The first answer that comes to mind is usually the weak one.

This free guide answers 16 of them properly.

On every page

• The question, as a concrete scenario
• The weak answer people tend to give
• The strong answer, in three short points
• The pitfall people still miss
• A follow-up to practise

Covers APIs, databases, reliability and production: idempotency, race conditions, N+1 queries, migrations, webhooks, caching, sessions and password storage.

Tool-specific details were checked against official docs (PostgreSQL, Python requests, OWASP). Not DSA, and not any company’s question list.

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