I started with a basic array-backed queue and talked through enqueue and dequeue, but they kept pushing on things like what happens with multiple consumers, ordering guarantees, and whether messages get acknowledged before removal.
Start by clarifying requirements (e.g., in-memory vs distributed, persistence, delivery guarantees) and then design a simple in-memory queue with core operations (enqueue, dequeue, peek, size). Discuss trade-offs of different data structures (e.g., linked list vs ring buffer) and concurrency handling, then extend to persistence and scaling if needed.
Pro tip: Demonstrate awareness of real-world message queue systems (like Kafka, RabbitMQ) by mentioning key features such as durability, ordering, and backpressure, but emphasize that you're building a simplified version to meet the stated requirements.
Ask about expected throughput, latency, persistence, delivery guarantees (at-least-once, at-most-once), and whether it's single-process or distributed. This shows you avoid assumptions and tailor the design.
Choose an appropriate data structure (e.g., linked list for unbounded queue, ring buffer for bounded) and implement basic operations: enqueue, dequeue, peek, isEmpty. Discuss time/space complexity.
Address thread safety using locks, condition variables, or lock-free algorithms. Explain how to avoid race conditions and ensure blocking/non-blocking behavior.
If required, discuss writing messages to disk (e.g., append-only log) and recovery mechanisms. Mention trade-offs between performance and durability.
Outline how to scale horizontally (partitioning, replication) and add features like message acknowledgment, dead-letter queues, and monitoring.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.