[petergeoghegan]

I hear that one from time to time. It's a consequence of the fact that sequences are generally not transactional, and the fact that the underlying "speculative insertion" infrastructure really does have to do most of the work of the insertion before it can decide whether or not the insertion really should go ahead.

I'm sympathetic, but unfortunately I cannot think of any tractable way of avoiding the problem at the implementation level. Maybe it would be possible to do something with an identity column (as opposed to a SERIAL column or a raw sequence) -- we have access to sufficient context there. Maybe we could skip consuming a sequence in the common case where there is a clear conflict at the start, and the sequence isn't accessed through the EXCLUDED pseudo table. We wouldn't actually promise anything more, but in practice we wouldn't burn through sequences at the same rate in cases where updates are common.

This is quite a significant project, but maybe it'll happen some day.