Step 4 - Wrap up

We discussed different approaches to design a unique ID generator: multi-master replication, UUID, ticket server, and Twitter snowflake-like unique ID generator. We settled on snowflake as it supports all our use cases and is scalable in a distributed environment.

If there is extra time at the end of the interview, here are a few additional talking points:

• Clock synchronization. In our design, we assume ID generation servers have the same clock. This assumption might not be true when a server runs on multiple cores. The same challenge exists in multi-machine scenarios. Solutions to clock synchronization are out of the scope of this book; however, it is essential to understand the problem exists. Network Time Protocol is the most popular solution to this problem. For interested readers, refer to the reference material.

• Section length tuning. For example, fewer sequence numbers but more timestamp bits are effective for low-concurrency and long-term applications.

• High availability. Since an ID generator is a mission-critical system, it must be highly available.