What I'd like to understand about this patch is how it relates
to Amit L.'s work on making the planner faster for partitioned
UPDATE/DELETE cases (https://commitfest.postgresql.org/22/1778/).
I think that that might render this moot? And if it doesn't,
how much does it really matter? You can't really postpone taking
a lock on a relation that the planner is going to do anything
nontrivial with.
regards, tom lane