...and then you additionally have to verify that the specific reason both the update and the insert failed was due to concurrency, or you can make the mistake I did a couple years ago where I had transactions spinning against my database for weeks on end due to an unrelated constraint failure I had failed to notice with some transactions that I kept retrying in a loop as part of my hacked together upsert implementation (which is why my user id numbers jumped from ~8m to ~460m... it is a meaningless mistake, but one I am reminded of every day due to that "46" staring at me :/).