ULID: Universally Unique Lexicographically Sortable Identifier

Whenever ULID comes up, I need to remind that it has a sequential ID generation mode in its spec which is prone to conflicts on multi-threads, processes or hosts which kills the purpose of a "universal" identifier. If you need a sequential ID, just use an integer, preferably one that's autoincremented by the database.

It's best to stick to UUIDv7 because of such quirks of ULID.

ULID's initial segment is timestamp generated, with a random suffix at the end. This kind of collision you're concerned about is not an issue at all, across multi-threads, processes or hosts.

Not if the same ULID generator instance is used across threads.

That depends on if the specific implementation of the generator instance is thread safe. Highly implausible to use the same generator instance between different threads/processes/hosts because there's no benefit at all and only additional downsides.

To implement a thread-safe sequential increment, you need locking. When you use locking, then it becomes a “non-universal” ID generator with arbitrary performance impact.

Either it’s collision-prone or locking. Both are problematic in their own way.

It’s footguns all over while UUIDv7 simply exists.