Andrei Lepikhov <a(dot)lepikhov(at)postgrespro(dot)ru> writes:
> "SET foo.bar TO 'smth'" can immediately alter the placeholder's value.
> But what is the reason that "ALTER SYSTEM SET foo.bar TO 'smth'" doesn't
> do the same?
Because it's not supposed to take effect until you issue a reload
command (and maybe not even then, depending on which GUC we're
talking about). I certainly think it wouldn't make sense for your
own session to adopt the value ahead of others.
regards, tom lane