> Uh, why exactly do you think this is race-free?
>
> It looks fancy, but AFAICS the SELECT will return info that is correct
> as of its starting timestamp; which is not enough to guarantee that the
> INSERT won't conflict with another transaction doing the same thing
> concurrently.
How about:
INSERT INTO table SELECT 1, 'foo' WHERE NOT EXISTS (SELECT TRUE FROM table
WHERE pkcol=1 FOR UPDATE);
It's a lot more straightforward and has a FOR UPDATE. Can this still cause
unique constraint failures?
Chris