On Wed, 1 Oct 2025 17:22:39 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: > > remove old test case reference src/java.base/share/classes/java/util/UUID.java line 207: > 205: * @return a {@code UUID} constructed using the given {@code > timestamp} > 206: * > 207: * @throws IllegalArgumentException if the timestamp is negative or > greater than {@code 281474976710655L} What would you think about using (1L << 48) - 1 instead? src/java.base/share/classes/java/util/UUID.java line 210: > 208: * > 209: * @spec https://www.rfc-editor.org/rfc/rfc9562.html > 210: * RFC 9562 Universally Unique IDentifiers (UUIDs) The updated class description means the class now has a prominent link to RFC, so not sure about having another link here. If we are linking then can we link to ##name-uuid-version-7. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2416732407 PR Review Comment: https://git.openjdk.org/jdk/pull/25303#discussion_r2416721464
