Staff Interview Questions

Design a database schema for an e-commerce platform that handles flash sales. During a flash sale, 10,000 users try to buy the last 100 units simultaneously. Your schema must prevent overselling. Show the schema and the critical query.

Design the backend for a live cricket score app. 50 million users are watching simultaneously, score updates every ball. Users must see the score update within 2 seconds.

Design a hotel booking system. Rooms must not be double-booked. Searches should show real-time availability. Handle 10,000 concurrent booking attempts for popular dates.

What is the Saga pattern in microservices? When would you choose choreography over orchestration?

What is a sidecar proxy and how does it work in service mesh architecture?

Design YouTube's video upload and processing pipeline. A user uploads a 4K video of 10GB. How does it become available in 360p, 720p, and 4K for streaming?

What is a service mesh and what problem does it solve that a regular load balancer doesn't?

Design a system that detects fraudulent credit card transactions in real-time (decision in under 50ms). The system processes 10,000 transactions per second.

Design a distributed job scheduler like AWS Batch. Jobs have dependencies (job B starts only after job A completes). The system must handle 100K jobs per day.

Design a rate limiter in Node.js that allows 100 requests per user per minute. It must work across multiple Node.js instances without a central Redis lock causing a bottleneck.

What is the N-API and why is it important for Node.js native addons? When would you write a native addon?

Implement Dijkstra's algorithm using a Fibonacci heap. Compare amortized complexity with a binary heap and explain when the Fibonacci heap is actually slower in practice despite the better theoretical bound.