The docs have always been slightly inaccurate, but got particularly so
in a874fe7b, which made DISCARD ALL occur before everything else;
reorder.

Author: Jan Chochol
Discussion: https://postgr.es/m/CAEASf_3TzBbnXm64HpnD5zCZEh8An9jN8ubMR=De-vOXHMHGeA@mail.gmail.com