On Thu, 9 Oct 2025 17:13:23 GMT, Kieran Farrell <[email protected]> wrote:
>> With the recent approval of UUIDv7 >> (https://datatracker.ietf.org/doc/rfc9562/), this PR aims to add a new >> static method UUID.timestampUUID() which constructs and returns a UUID in >> support of the new time generated UUID version. >> >> The specification requires embedding the current timestamp in milliseconds >> into the first bits 0–47. The version number in bits 48–51, bits 52–63 are >> available for sub-millisecond precision or for pseudorandom data. The >> variant is set in bits 64–65. The remaining bits 66–127 are free to use for >> more pseudorandom data or to employ a counter based approach for increased >> time percision >> (https://www.rfc-editor.org/rfc/rfc9562.html#name-uuid-version-7). >> >> The choice of implementation comes down to balancing the sensitivity level >> of being able to distingush UUIDs created below <1ms apart with performance. >> A test simulating a high-concurrency environment with 4 threads generating >> 10000 UUIDv7 values in parallel to measure the collision rate of each >> implementation (the amount of times the time based portion of the UUID was >> not unique and entries could not distinguished by time) yeilded the >> following results for each implemtation: >> >> >> - random-byte-only - 99.8% >> - higher-precision - 3.5% >> - counter-based - 0% >> >> >> Performance tests show a decrease in performance as expected with the >> counter based implementation due to the introduction of synchronization: >> >> - random-byte-only 143.487 ± 10.932 ns/op >> - higher-precision 149.651 ± 8.438 ns/op >> - counter-based 245.036 ± 2.943 ns/op >> >> The best balance here might be to employ a higher-precision implementation >> as the large increase in time sensitivity comes at a very slight performance >> cost. > > Kieran Farrell has updated the pull request incrementally with one additional > commit since the last revision: > > update spec src/java.base/share/classes/java/util/UUID.java line 74: > 72: * > 73: * @spec https://www.rfc-editor.org/rfc/rfc9562.html > 74: * RFC 9562 Universally Unique IDentifiers (UUIDs) Hello Kieran, In this class there's a pre-existing `variant()` method. On that method, the javadoc still refers to RFC-4122. Please update `<a href...` link in that javadoc to use RFC-9562 like you have done here and please also remove the `@spec` from that method's javadoc. I don't think it's needed there, given that it will link to the RFC as well as this class level `@spec` test/jdk/java/util/UUID/UUIDTest.java line 150: > 148: } > 149: > 150: private static void epochMillis_userInputTest() { Nit - it might be better to name this method `testEpochMillisTimestamp()` test/jdk/java/util/UUID/UUIDTest.java line 159: > 157: } > 158: } catch (Exception e) { > 159: throw new AssertionError("Unexpected exception with > timestamp " + timestamp + ": " + e); Please pass the original exception `e` as the cause of this AssertionError, something like: throw new AssertionError("Unexpected exception with timestamp " + timestamp, e); That will help debug any failures if at all they happen. Same comment for a few other places in this new test method. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2452711341 PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2452716220 PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2452715029
