Add support for UUID version 7 #19
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FYI: see an earlier PR here: #15. I wasn't aware of that other PR when I first started on mine. The primary distinction from that PR is that this allows up to 12 extra bits of timestamp precision, at the cost of code complexity. |
| # {Section 6.2}[https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bis-07.html#monotonicity_counters] | ||
| # of the specification. | ||
| # | ||
| def uuid_v7(extra_timestamp_bits: 0) |
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Any suggestions for a better keyword parameter name?
nevans
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| rand.unpack("H4H12").join("-") | ||
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| when (0..12) # the generic version is slower than the special cases above |
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I don't know. :) I can go either way:
- On the one hand, because 0 and 12 are handled by the prior clauses, it makes sense to only show the numbers that will be handled by this clause.
- On the other hand, since this is the generic version, it can handle 0..12, and it's nice to "document" that here.
Although I did consider this earlier, I think I left it as 0..12 mostly by accident: While I was testing and benchmarking the code, I would copy/paste the entire method and then comment out or delete one of the other clauses. So it was temporarily simpler to keep this as 0..12.
So, what do you think?
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Any updates on this or sibling for including UUIDv7 support? |
| # | ||
| # See draft-ietf-uuidrev-rfc4122bis[https://datatracker.ietf.org/doc/draft-ietf-uuidrev-rfc4122bis/] | ||
| # for details of UUIDv7. | ||
| # |
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@nevans It would be good to note that fixing the random number seed (e.g., by Kernel#srand) does not make this method reproducible.
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Good point. I'll add a note for that. If I remember correctly, I had originally written a version that allowed a keyword argument for the timestamp. But when I changed the code to allow extra_timestamp_bits, it didn't seem like it was worth the complexity.
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What do you think about the following:
| # | |
| # | |
| # Note that this method cannot be made reproducable with Kernel#srand, which | |
| # can only affect the random bits. The sorted bits will still be based on | |
| # Process.clock_gettime. | |
| # |
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@nevans Ah, there are some other ways to fix the random seed than Kernel#srand, such as: Random.new(0).uuid_v7.
How about this? This PR is already merged, so I will create another PR if you are OK.
Note that this method cannot be made reproducable because its output includes not only random bits but also timestamp.
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@mame Looks good. I like your text better than mine. It's simpler, clearer, and covers the Random.new(0) scenario too. :)
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@nevans Thank you for submitting this. Can you confirm #19 (comment)? I'll merge this after that. |
I pushed a new version with the change I suggested here: #19 (comment). Is that good? |
Although the specification for UUIDv7 is still in draft, the UUIDv7 algorithm has been relatively stable as it progresses to completion. Version 7 UUIDs can be very useful, because they are lexographically sortable, which can improve e.g: database index locality. See section 6.10 of the draft specification for further explanation: https://datatracker.ietf.org/doc/draft-ietf-uuidrev-rfc4122bis/ The specification allows up to 12 bits of extra timestamp precision, to make UUID generation closer to monotonically increasing. This provides between 1ms and ~240ns of timestamp precision. At the cost of some code complexity and a small performance penalty, a kwarg may specify any arbitrary precision between 0 and 12 extra bits. Any stronger guarantees of monotonicity have considerably larger tradeoffs, so nothing more is implemented. This limitation is documented. Ruby issue: https://bugs.ruby-lang.org/issues/19735
Although the specification for UUIDv7 is still in draft, the UUIDv7 algorithm has been relatively stable as it progresses to completion.
Version 7 UUIDs can be very useful, because they are lexographically sortable, which can improve e.g: database index locality. See section 6.10 of the draft specification for further explanation:
https://datatracker.ietf.org/doc/draft-ietf-uuidrev-rfc4122bis/
The specification allows up to 12 bits of extra timestamp precision, to make UUID generation closer to monotonically increasing. This provides between 1ms and ~240ns of timestamp precision. At the cost of some code complexity and a small performance penalty, a kwarg may specify any arbitrary precision between 0 and 12 extra bits. Any stronger guarantees of monotonicity have considerably larger tradeoffs, so nothing more is implemented. This limitation is documented.
Ruby issue: https://bugs.ruby-lang.org/issues/19735