=?utf-8?Q?Andr=C3=A9_H=C3=A4nsel?= <andre(at)webkr(dot)de> writes:
> This will yield “8”, showing that new sequence numbers have been generated for each attempt.
Well, yeah, because the INSERT has to be attempted first, and
that includes forming the whole candidate row including the
nextval() result. If you're expecting a serial ID column to not
have holes in the sequence of values, you're going to be sadly
disappointed, whether you use ON CONFLICT UPDATE or not.
regards, tom lane