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    The problem is in detecting collisions — if we could detect them instantly, we would not release those that collided and regenerate a new one right away, so the caller would never even see the throw. Commented Jan 15, 2024 at 23:04
  • @ErikEidt - if you throw this kind of error once per your lifetime, you would be lucky man. So its fine to just risk it. Commented Jan 16, 2024 at 11:03
  • If you throw this error once in your lifetime, that’s too often. But anyway, check out whether throwing an exception (with absolutely untested handling) or just ignoring the collision is worse. It’s quite possible that a collision with another UUID generated ten years ago will have no negative effect at all. Commented Jan 16, 2024 at 22:37
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    Even though the probability of randomly picking the same UUID twice is astronomically low, you usually have to carefully consider what would happen when there are collisions anyway, not "just risk it". Even if you throw an exception inserting the record, what state is the (distributed!) system in after that exception; is it valid, or vulnerable to attack? Are you sure that no other records were inserted assuming they were referring to the one that was rejected that are actually now referring to the other one that tried to use that id? Commented Jan 17, 2024 at 2:21
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    Because collisions can happen due to clients that are erroneous or malicious, not just due to the RNG actually rolling the same UUID again. You generally can't assume the probability of that is near-zero (especially malicious clients). This point applies to schemes that guarantee uniqueness too though; if you can't assume all clients are non-malicious and bugfree, you have to deal with potential collisions anyway. Commented Jan 17, 2024 at 2:22