58 lines
3.8 KiB
Plaintext
58 lines
3.8 KiB
Plaintext
UuidGenerator.Style values and what the generated UUIDs look like. Hibernate 7.4.14.Final, JDK 25.0.3+9-LTS-195
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== The enum and the annotation, from the shipped jar
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Style values : [AUTO, RANDOM, TIME, VERSION_6, VERSION_7]
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annotation attributes : [algorithm, style]
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== Does the JDK itself generate version 7? (public static methods of java.util.UUID)
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static factories: [fromString, nameUUIDFromBytes, randomUUID]
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== GenerationType.UUID (JPA) (UuidV4Item, 2000 persists in one transaction)
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first three : [5b257f75-63bc-4f48-905d-65bac3459d13, 8b636cac-72ba-4740-baa4-960522598e0f, 7563a4d5-dfe5-4be5-b1f5-55e71a83eaec]
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version nibble of every id : [4], variant : [2]
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string/byte order vs generation order : 1017 of 1999 neighbours are out of order
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== bare @GeneratedValue on a UUID (AUTO) (AutoUuidItem, 2000 persists in one transaction)
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first three : [35ad5be5-7f04-4dc8-83b9-f2266e101ab0, 78a0cefb-b172-46e4-94aa-60212ad0b190, 162be54a-33b8-4018-8df9-5e43836cc2af]
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version nibble of every id : [4], variant : [2]
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string/byte order vs generation order : 1005 of 1999 neighbours are out of order
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== Style.TIME (UuidTimeItem, 2000 persists in one transaction)
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first three : [c0a802bb-a1ad-1754-81a1-ad076a3225a0, c0a802bb-a1ad-1754-81a1-ad076a3225a1, c0a802bb-a1ad-1754-81a1-ad076a3225a2]
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version nibble of every id : [1], variant : [2]
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string/byte order vs generation order : 0 of 1999 neighbours are out of order
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UUID.timestamp() of first / last id (100ns ticks since 1582) : 528224823942841019 / 528224823942841019
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most significant 32 bits (time_low) of first three : [c0a802bb, c0a802bb, c0a802bb]
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== Style.VERSION_6 (UuidV6Item, 2000 persists in one transaction)
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first three : [1f1d9490-534d-6627-8be9-341e19966c04, 1f1d9490-534d-6627-8bea-9c10655ddb7b, 1f1d9490-534d-6627-8beb-b5f923905e48]
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version nibble of every id : [6], variant : [2]
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string/byte order vs generation order : 0 of 1999 neighbours are out of order
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== Style.VERSION_7 (UuidV7Item, 2000 persists in one transaction)
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first three : [01a1ad07-6af9-7f60-91e5-a074a2e61b15, 01a1ad07-6af9-7f60-bafb-92ecaabdd57e, 01a1ad07-6af9-7f61-84be-68a7813aa2e1]
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version nibble of every id : [7], variant : [2]
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string/byte order vs generation order : 0 of 1999 neighbours are out of order
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first 48 bits as Unix milliseconds : 1793904306937 -> 2026-11-05T18:45:06.937Z
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== uuid-creator getTimeOrderedEpoch() (UuidCreatorV7Item, 2000 persists in one transaction)
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first three : [01a1ad07-6b4a-7727-8708-c7b485cd7cc5, 01a1ad07-6b4a-7727-8709-75a505ff49d2, 01a1ad07-6b4a-7727-870a-1991eca1f5b5]
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version nibble of every id : [7], variant : [2]
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string/byte order vs generation order : 0 of 1999 neighbours are out of order
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first 48 bits as Unix milliseconds : 1793904307018 -> 2026-11-05T18:45:07.018Z
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== hand-written UuidV7Generator (HandRolledV7Item, 2000 persists in one transaction)
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first three : [01a1ad07-6ba5-7041-a4e3-8df974d6a001, 01a1ad07-6ba5-7042-8be9-c72dadba0e18, 01a1ad07-6ba5-7043-87de-73e7de8dbb54]
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version nibble of every id : [7], variant : [2]
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string/byte order vs generation order : 0 of 1999 neighbours are out of order
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first 48 bits as Unix milliseconds : 1793904307109 -> 2026-11-05T18:45:07.109Z
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== Style.TIME is not a clock-ordered v1: what changes between ids created 30 ms apart
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c0a802bb-a1ad-1754-81a1-ad076be82d70 msb=c0a802bba1ad1754 lsb=81a1ad076be82d70
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c0a802bb-a1ad-1754-81a1-ad076c092d71 msb=c0a802bba1ad1754 lsb=81a1ad076c092d71
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c0a802bb-a1ad-1754-81a1-ad076c282d72 msb=c0a802bba1ad1754 lsb=81a1ad076c282d72
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c0a802bb-a1ad-1754-81a1-ad076c482d73 msb=c0a802bba1ad1754 lsb=81a1ad076c482d73
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distinct most-significant halves among them : 1 (IPv4 address of this host + a per-JVM value, fixed for the life of the JVM)
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first 32 bits equal this host's IPv4 address : true
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UUID.timestamp() (what a real version 1 would use as its clock) is the same for all four : 1 distinct value(s)
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