Leveraging ULIDs to create order in unordered datastores

The rise of distributed data stores and the general decomposition of systems into smaller pieces means that coordination between each server, service, or function is less available. In my first applications, unique ID generation meant setting auto_increment=True on a column in the SQL database. Easy, done, no problem. Today, each microservice has its own data source(s) and NoSQL stores are common. Every NoSQL DB is “NoSQL” in its own way, but they usually eschew coordinated and single-writer solutions in the name of reliability/performance/both. You can’t have an auto-increment column without implementing the coordination client-side.

Using numbers as identifiers also creates problems. Auto-incrementing can lead to enumeration-based attacks. Fields can have fixed sizes. These issues can go unrealized until you overflow the uint32 field, and now your logs are a pile of ID conflict errors. Instead of integers, we can use a different kind of fixed-length field and make it non-sequential so that different hosts can generate IDs without a central coordinating point.

UUID’s are an improvement and avoid collisions in distributed settings, but being strictly random you don’t have a way to easily sort them or determine rough order. Segment blogged a while ago about one replacement for UUIDs with the KSUID (K-Sortable Universal ID) but it has limitations and uses a strange 14e8 offset to avoid running out of epoch time in the next 100 years.

Enter the Unique Lexicographically Sortable Identifier (ULID). These are sortable, high-entropy identifiers that we can generate anywhere in our pipeline without coordination and have confidence that there won’t be collisions. A ULID looks like 01E5TZRCM5WZYPB2BH7KMYR5HT, and the first 10 characters are a timestamp, and the next 16 characters are random.

https://www.trek10.com/blog/leveraging-ulids-to-create-order-in-unordered-datastores