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uuid-rs / uuid

Generate and parse UUIDs.
https://www.crates.io/crates/uuid
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Support counters in v7 UUIDs #755

Closed KodrAus closed 4 months ago

KodrAus commented 6 months ago

For #717

This PR sketches out a solution to make the v7 support respect the input counter, while retaining existing semantics around filling with random data. It requires a bit of fudgery to keep compatibility with existing APIs, but I think the overall solution works out ok. I need to actually fill it all in fully and then explore ways to better integrate the existing Timestamp API, which may involve deprecating bits.

The gist of it is to add a usable_bits method to ClockSequence, so it can tell how many bits a given counter occupies. The UUID constructor can then do appropriate shifts and fill the rest with random bytes. That way a caller creating a v7 UUID can decide how many bits to dedicate to sequencing and how many to randomness.

As part of this PR I'm expecting to find some solution to re-seeding sequences, which will probably remain an implementation detail of the given ClockSequence.

KodrAus commented 4 months ago

I've got a counter implemented, but looks like performance here could use some improvement compared to uuid7:

running 2 tests
test new_v4   ... bench:          24.69 ns/iter (+/- 0.43)
test uuid7_v4 ... bench:          14.31 ns/iter (+/- 0.06)

test now_v7   ... bench:          56.86 ns/iter (+/- 1.04)
test uuid7_v7 ... bench:          38.03 ns/iter (+/- 0.59)
KodrAus commented 4 months ago

Ok, I think that's better now:

test new_v4   ... bench:           8.35 ns/iter (+/- 0.34)
test uuid7_v4 ... bench:          14.38 ns/iter (+/- 0.78)

test now_v7   ... bench:          36.51 ns/iter (+/- 2.60)
test uuid7_v7 ... bench:          38.31 ns/iter (+/- 2.35)
KodrAus commented 4 months ago

I need to add some tests for the new v7 context, and make sure we're shifting it around the variant field correctly.