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.

> 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.

Can you expand on how this can actually cause a problem? My understanding is different processes and hosts should never conflict because of the 80 bits of random data. The only way I can conceive of a conflict is multiple threads using the same non-thread-safe generator during the same millisecond.

You're right, not hosts or processes in that case. I forgot about random part as it's been a while since I looked at it. However, a single instance of a ULID generator must support this mode, which means that on multi-threaded architectures, it must lock the sequence as it still uses a single random value. That again, kills the purpose of a client-side, lock-free generation of universal identifiers as you said.