> However if you want any sort of efficient lookup on the external key (UUID), your database still needs an index on the UUID, and you are back at square one.

> However if you want any sort of efficient lookup on the external key (UUID), your database still needs an index on the UUID, and you are back at square one. Well. Many systems already do a form of this. They store a session ID (the browser cookie) in something like redis which maps to an internal database id which is often incremented. The internal database ids are never seen outside the DB. In this case it's fine because the external IDs are ephemeral (relatively) and centralization is a hard criteria (you typically can't have two people creating an account with the same user name, or having one email address linked to multiple record IDs, etc.). This is really why these discussions are pointless without specifics and a concrete system.