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I'm wondering if UUIDs are unique even when they are generated on different systems, which may employ different algorithms. For instance, if you generated a bunch of UUIDs in MySQL, and .Net, would there be a higher chance of collision, or are all systems using the exact same algorithm, and thereby guaranteeing that collisions are improbable?
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A collision is possible but the total number of unique keys generated is so large that the possibility of a collision is almost zero. As per Wikipedia, the number of UUIDs generated to have atleast 1 collision is 2.71 quintillion.
The UUID relies on a combination of components to ensure uniqueness. UUIDs are constructed in a sequence of digits equal to 128 bits. The ID is in hexadecimal digits, meaning it uses the numbers 0 through 9 and letters A through F.
No, a UUID can't be guaranteed to be unique. A UUID is just a 128-bit random number. When my computer generates a UUID, there's no practical way it can prevent your computer or any other device in the universe from generating that same UUID at some time in the future.
It's possible to generate an identical guid over and over. However, the chances of it happening are so low that you can assume they are unique.
From Universally unique identifier on Wikipedia: ..the word unique should be taken to mean "practically unique" rather than "guaranteed unique". Since the identifiers have a finite size it is possible for two differing items to share the same identifier. The identifier size and generation process need to be selected so as make this practically impossible.
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