Even if it is a hair slower, UUIDs (or similar schemes) are advantageous for reasons beyond being able to merge tables.<p>Another big advantage is being able to use the UUID as a key, without worrying about exploits from guessing serial numbers:<p><a href="https://en.wikipedia.org/wiki/Predictable_serial_number_attack" rel="nofollow">https://en.wikipedia.org/wiki/Predictable_serial_number_atta...</a>