Forgot to add (all seen in production):

* Don't store UUIDs as strings.

* Don't use random UUID variants for your primary key (or don't use UUIDs for your primary key).

* Don't use a random column in your clustered index.

I guess things are DB dependent. Spanner for instance not only recommends using uuidv4 as a PK, it also stores it as string(36). Uuidv4 as a PK works fine on Postgres as well.