This serves as a write-through cache for caching the namespace and tablename as they occur in PG.

Note that if users create shapes for the same table but spelled differently, e.g. ~s|public.users|, ~s|users|, ~s|Users|, and ~s|USERS| then there will be 4 entries in the cache each of which maps to {~s|public|, ~s|users|}. If they create a shape for a different table ~s|"Users"|, then there will be another entry in ETS for ~s|"Users"| that maps to {~s|public|, ~s|"Users"|}.