The previous version of the docs mentioned that files are rewritten,
implying that a second copy of each file gets created, but each file is
updated in-place.

Author: Michael Banck
Reviewed-by: Daniel Gustafsson, Michael Paquier
Discussion: https://postgr.es/m/858086b6a42fb7d17995b6175856f7e7ec44d0a2.camel@credativ.de
Backpatch-through: 12