Tatsuo Ishii <t-ishii(at)sra(dot)co(dot)jp> writes:
> Once I thought of a conversion lookup cache, but it seems impossible
> to implent it since the cache needs to be invalidated when the schema
> search path is changed.
On the contrary, that seems very easy to do. There is a hook to let you
get control whenever a syscache inval event is received. Look at the
way that namespace.c arranges to invalidate its cache of the search
path OIDs whenever pg_namespace is modified.
regards, tom lane