Started with the obvious stuff, a simple delay queue, but the interviewer kept pushing on scale.
Start by clarifying the scope: what kind of timer system (e.g., for scheduling tasks, UI countdowns, or distributed timeouts) and the scale requirements. Then propose a high-level design, focusing on core components like a priority queue or timing wheel, and discuss trade-offs between accuracy, scalability, and resource usage.
Pro tip: Demonstrate awareness of real-world constraints by mentioning how you'd handle persistence and recovery, and how you'd monitor and alert on timer drift or failures.
Ask questions to understand the use case, scale, accuracy needs, and constraints (e.g., single-node vs distributed, persistence required).
Outline the main components: timer registration, storage of timers, and a mechanism to trigger callbacks at the right time.
Choose and justify a data structure (e.g., min-heap, timing wheel) and discuss how to handle concurrency, persistence, and scalability.
Compare different approaches (e.g., heap vs timing wheel) in terms of time complexity, memory, and suitability for different scales.
Cover failure scenarios, recovery, monitoring, and how to ensure timers fire correctly even under load or failures.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.