An additional thing I learned when I worked on a ulid alternative over the weekend[0] is: Postgres's internal Datum type is at most 64 bits which means every uuid requires heap allocation[1] (at least until we get 128 bit machines).

0: https://bsky.app/profile/hugotunius.se/post/3m7wvfokrus2g

1: https://github.com/postgres/postgres/blob/master/src/backend...