As it turns out, c_lo_creat, etc. are just wrappers around PQfn to the corresponsing server-side functions. Also, there is no non-blocking variant of PQfn in libpq, though a protocol-level client could certainly support fast-path calls with a non-blocking implementation. Thus as postgresql-simple moves to a non-blocking implementation underneath the library, it will make sense to eventually abandon the large object binding in postgresql-libpq in favor of non-blocking calls to execParams.