My first instinct was a simple counter but they pushed back pretty fast on that.
Start by clarifying requirements (scale, persistence, concurrency, ID format) and then propose a design that balances simplicity, performance, and reliability. Walk through the core data structures and algorithms for allocation and reclamation, then discuss trade-offs and failure handling.
Pro tip: Mention that ID reclamation can lead to security and debugging issues (e.g., stale references), so consider a generation counter or delayed reuse. Also, discuss how to handle ID exhaustion and whether IDs should be globally unique or just unique within a pool.
Ask about scale (IDs per second, total pool size), persistence needs, concurrency, and whether IDs must be globally unique or can be reused immediately. Also clarify if IDs need to be numeric, sequential, or can be arbitrary.
Propose a module with two main operations: allocate() and release(id). Outline the components: an ID generator, a free list (or pool) for reclaimed IDs, and a persistent store if needed. Discuss whether to use a centralized service or a distributed approach.
Detail how to efficiently allocate and reclaim IDs. For allocation, consider using a queue or stack for free IDs, and a counter for new IDs. For reclamation, add the ID back to the free list. Discuss thread-safety using locks or lock-free structures.
Compare approaches: in-memory vs. persistent, centralized vs. distributed, immediate reuse vs. delayed reuse. Discuss trade-offs in terms of latency, throughput, consistency, and complexity. Mention how to handle ID exhaustion and failure recovery.
Cover edge cases: double release, releasing invalid IDs, concurrent allocation/release, and system crashes. Propose solutions like idempotent release, validation, and write-ahead logging for persistence.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.