I wrote
> That's what I did at first, but later I found better performance with
> a TRIGGER on the permanent table that deletes the target of an UPDATE,
> if any, before the UPDATE. [INSERT!] That's what PG does anyway, and now I can do
> the entire UPDATE [INSERT] in one command.
It's probably obvious, but what I should have said is that now I do the INSERT in one command; I have no need of an UPDATE. So I do no UPDATEs, only INSERTs.