My Paytm Backend Engineer Technical Round (Noida, 2.8 YOE) – Full Questions + Takeaways

Just finished my 45-minute Backend Engineer technical round at Paytm (Noida).Process was quick via Naukri recruiter.Round started with “Tell me about yourself” + deep dive on my fintech projects (wall

Just finished my 45-minute Backend Engineer technical round at Paytm (Noida).Process was quick via Naukri recruiter.Round started with “Tell me about yourself” + deep dive on my fintech projects (wallet service, Razorpay integration, Kafka events).Core Java + Spring Boot: * Functional Interface with real example * u/Async vs synchronized block (differences & use cases) * u/Transactional (class vs method level + rollback scenarios) * u/Repository vs u/Service vs u/Component – when to use each * How Dependency Injection works internally in Spring Boot * HashMap internals, ArrayList vs LinkedList, Stack & Queue practical use-cases System Design & Architecture (main focus): * Full JWT flow: login → token generation & storage → logout behaviour → token expiry * Rate Limiting + deep dive on Token Bucket algorithm (they asked specifically about the one I implemented in project) * Cron job in multi-instance setup: How to make sure only one instance runs the job? * RabbitMQ vs Kafka differences + when to choose which * Event-Driven Architecture and how it achieves decoupling Coding Question (last 10 mins): List of bank accounts (account type + balance) → find all accounts with balance > 10,000 and group/filter by account type.My Takeaways: * Super practical round – focused on real-world backend concepts used at fintech scale (Spring internals, security, distributed systems, messaging). * No heavy LeetCode DSA or full LLD/HLD. * I felt confident because I revised these exact topics the night before. Waiting for result/next round. Will update here.If anyone is preparing for Paytm or similar backend roles, feel free to ask in comments – happy to share more details or the resources I used.