Which UUID version to use?

Question

Which version of the UUID should you use? I saw a lot of threads explaining what each version entails, but I am having trouble figuring out what's best for what applications.

Answer 1

There are two different ways of generating a UUID.

If you just need a unique ID, you want a version 1 or version 4.

• Version 1: This generates a unique ID based on a network card MAC address and current time. If any of these things is sensitive in any way, don't use this. The advantage of this version is that, while looking at a list of UUIDs generated by machines you trust, you can easily know whether many UUIDs got generated by the same machine, or infer some time relationship between them.

• Version 4: These are generated from random (or pseudo-random) numbers. If you just need to generate a UUID, this is probably what you want. The advantage of this version is that when you're debugging and looking at a long list of information matched with UUIDs, it's quicker to spot matches.

If you need to generate reproducible UUIDs from given names, you want a version 3 or version 5.

• Version 3: This generates a unique ID from an MD5 hash of a namespace and name. If you need backwards compatibility (with another system that generates UUIDs from names), use this.

• Version 5: This generates a unique ID from an SHA-1 hash of a namespace and name. This is the more secure version.