Adjustments requested by reviewers.

Reported-by: Amit Kapila, Thomas Munro, Andrew Gierth, Amit Langote, Oleg Bartunov, Michael Paquier, Alvaro Herrera, Tatsuo Ishii

Discussion: https://postgr.es/m/20190506233029.ozwged67i7s4qd6c@momjian.us