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51 lines
4.4 KiB
51 lines
4.4 KiB
3 weeks ago
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[ntietz.com](https://ntietz.com/blog/til-uses-for-the-different-uuid-versions/)
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# TIL: 8 versions of UUID and when to use them
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3–4 minutes
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---
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**Saturday, June 29, 2024**
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About a month ago[1](about:reader?url=https%3A%2F%2Fntietz.com%2Fblog%2Ftil-uses-for-the-different-uuid-versions%2F#not-today), I was onboarding a friend into one of my side project codebases and she asked me why I was using a particular type of UUID. I'd heard about this type while working on that project, and it's really neat. So instead of hogging that knowledge for just us, here it is: some good uses for different versions of UUID.
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## What are the different versions?
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Usually when we have multiple numbered versions, the higher numbers are newer and presumed to be better. In contrast, there are 8 UUID versions (v1 through v8) which are different and all defined in [the standard](https://datatracker.ietf.org/doc/html/rfc9562).
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Here, I'll provide some explanation of what they are at a high level, linking to the specific section of the RFC in case you want more details.
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- [UUID Version 1 (v1)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-1) is generated from timestamp, monotonic counter, and a MAC address.
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- [UUID Version 2 (v2)](https://datatracker.ietf.org/doc/html/rfc9562#name-uuid-version-2) is reserved for security IDs with no known details[2](about:reader?url=https%3A%2F%2Fntietz.com%2Fblog%2Ftil-uses-for-the-different-uuid-versions%2F#dce).
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- [UUID Version 3 (v3)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-3) is generated from MD5 hashes of some data you provide. The RFC suggests DNS and URLs among the candidates for data.
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- [UUID Version 4 (v4)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-4) is generated from entirely random data. This is probably what most people think of and run into with UUIDs.
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- [UUID Version 5 (v5)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-5) is generated from SHA1 hahes of some data you provide. As with v3, the RFC suggests DNS or URLs as candidates.
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- [UUID Version 6 (v6)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-6) is generated from timestamp, monotonic counter, and a MAC address. These are the same data as Version 1, but they change the order so that sorting them will sort by creation time.
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- [UUID Version 7 (v7)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-7) is generated from a timestamp and random data.
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- [UUID Version 8 (v8)](https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-8) is entirely custom (besides the required version/variant fields that all versions contain).
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## When should you use them?
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With eight different versions, which should you use? There are a few common use cases that dictate which you should use, and some have been replaced by others.
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You'll usually be picking between two of them: v4 or v7. There are also some occasions to pick v5 or v8.
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- Use v4 when you just want a random ID. _This is a good default choice._
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- Use v7 if you're using the ID in a context where you want to be able to sort. For example, consider using v7 if you are using UUIDs as database keys.
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- v5 or v8 are used if you have your own data you want in the UUID, but generally, you will know if you need it.
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What about the other ones?
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- [Per the RFC](https://www.rfc-editor.org/rfc/rfc9562.html#section-5.7-4), v7 improves on v1 and v6 and should be used over those if possible. So you usually won't want v1 or v6. If you do want one of those, you _can_ use v6.
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- v2 is reserved for unspecified security things. If you _are_ using these, you probably can't tell me or anyone else about it, and you're probably not reading this post to figure out more about them.
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- v3 is superceded by v5, which uses a stronger hash. This one is one where you probably _know_ if you need it.
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---
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---
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If this post was enjoyable or useful for you, **please share it!** If you have comments, questions, or feedback, you can email [my personal email](mailto:me@ntietz.com). To get new posts and support my work, subscribe to the [newsletter](https://ntietz.com/newsletter/). There is also an [RSS feed](https://ntietz.com/atom.xml).
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