This is basically the Snowflake ID question and I knew the shape of it going in, which helped.
Start by clarifying requirements (throughput, latency, sortability, availability) and then propose a Snowflake-like 64-bit ID layout: timestamp, machine ID, and sequence. Discuss how to assign machine IDs, handle clock skew and rollback, and shard the ID generation service for scalability. Finally, cover failure scenarios and trade-offs.
Pro tip: Emphasize that clock rollback is inevitable in distributed systems; propose a solution like waiting until the clock catches up or using a monotonic clock, and mention that duplicate machine IDs can be avoided with a coordination service like ZooKeeper or etcd. Also, highlight that sortability by time is often desired for database indexing.
Ask about expected throughput, latency, sortability, and availability requirements. Determine if IDs need to be roughly time-ordered and if the system must be globally unique across data centers.
Propose a 64-bit layout: 1 sign bit (0), 41 bits timestamp (ms since custom epoch), 10 bits machine ID, 12 bits sequence. This allows ~69 years, 1024 machines, and 4096 IDs per ms per machine.
Use a coordination service (ZooKeeper, etcd) to assign unique machine IDs. For clock rollback, either wait until clock catches up or use a monotonic clock; for clock skew, use NTP and allow small drift.
Deploy multiple instances of the ID generator, each with a unique machine ID. Shard by machine ID or use a load balancer to distribute requests. Consider a separate service for ID generation or embed in application.
Discuss handling duplicate machine IDs (e.g., via leases), clock rollback (e.g., fail fast or wait), and network partitions. Compare with UUIDs and other approaches.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.