Perhaps I was unclear, my underlying point is that short strings are
cheap. And enum names are almost always short strings. 4 characters not enough? What about 8? That’s the size of a BIGINT, which everybody now uses for primary keys (they’re not slow). What about 16 characters? That’s the size of a UUID, which everyone now uses for primary keys (they’re not slow).
Even 4 characters (which perform just as fast as Postgres’ native enums) is enough if you develop a system of abbreviations. The airline industry gets by with just three characters!
