Per the discussion at
https://www.postgresql.org/message-id/flat/54dfd2022c205eda9aa35b88923f027a%40postgrespro.ru
it's become evident that use of --disable-float8-byval breaks at least one
current regression test case, because it results in a large change in hash
table size for float8 hash keys. While we could hack around that somehow,
I think it would be a poor use of development effort. I have a modest
substitute proposal: let's just drop the --disable-float4-byval and
--disable-float8-byval configure options as of v11. Those don't have any
impact on on-disk storage. As best I can recall, the whole argument
for having them was to allow building backends that retained backwards
compatibility with old version-0 C functions that might expect pass-
by-reference behavior for these types. Now that we've dropped version-0
C function support, there's no point in that; any version-1 function that
is written per conventions won't notice the difference. So the extra
complication isn't buying useful flexibility, just more cases that we'd
have to test if we want to claim that we're supporting these options in
any meaningful way.
We would need to double-check that pg_upgrade allows converting from
byref to byval cases, but offhand I see no check for that in its code,
so I think it will just work.
(You might be wondering why these flags are reflected in pg_control,
if there's no impact on on-disk storage. The reason is that the backend's
compiled-in assumptions have to match what pg_type.typbyval says, so
pg_control memorializes what initdb put into the catalogs. But we should
be able to cope with changing that during a pg_upgrade cycle, just like
other catalog content changes.)
regards, tom lane