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Ben Ramsey
68 lines
2.5 KiB
ReStructuredText
68 lines
2.5 KiB
ReStructuredText
.. _rfc4122:
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==============
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RFC 4122 UUIDs
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==============
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.. toctree::
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:titlesonly:
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:hidden:
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rfc4122/version1
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rfc4122/version2
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rfc4122/version3
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rfc4122/version4
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rfc4122/version5
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rfc4122/version6
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rfc4122/version7
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rfc4122/version8
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`RFC 4122`_ defines five versions of UUID, while a `new Internet-Draft under
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review`_ defines three new versions. Each version has different generation
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algorithms and properties. Which one you choose depends on your use-case. You
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can find out more about their applications on the specific page for that version.
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Version 1: Gregorian Time
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This version of UUID combines a timestamp, node value (in the form of a MAC
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address from the local computer's network interface), and a clock sequence
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to ensure uniqueness. For more details, see :doc:`rfc4122/version1`.
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Version 2: DCE Security
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This version of UUID is the same as Version 1, except the ``clock_seq_low``
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field is replaced with a *local domain* and the ``time_low`` field is
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replaced with a *local identifier*. For more details, see
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:doc:`rfc4122/version2`.
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Version 3: Name-based (MD5)
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This version of UUID hashes together a namespace and a name to create a
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deterministic UUID. The hashing algorithm used is MD5. For more details, see
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:doc:`rfc4122/version3`.
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Version 4: Random
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This version creates a UUID using truly-random or pseudo-random numbers. For
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more details, see :doc:`rfc4122/version4`.
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Version 5: Named-based (SHA-1)
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This version of UUID hashes together a namespace and a name to create a
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deterministic UUID. The hashing algorithm used is SHA-1. For more details,
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see :doc:`rfc4122/version5`.
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Version 6: Reordered Time
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This version of UUID combines the features of a
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:ref:`version 1 UUID <rfc4122.version1>` with a *monotonically increasing*
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UUID. For more details, see :ref:`rfc4122.version6`.
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Version 7: Unix Epoch Time
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This version of UUID combines a timestamp--based on milliseconds elapsed
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since the Unix Epoch--and random bytes to create a monotonically increasing,
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sortable UUID without the privacy and entropy concerns associated with
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version 1 and version 6 UUIDs. For more details, see :ref:`rfc4122.version7`.
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Version 8: Custom
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This version of UUID allows applications to generate custom identifiers in
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an RFC-compatible format. For more details, see :doc:`rfc4122/version8`.
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.. _RFC 4122: https://tools.ietf.org/html/rfc4122
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.. _new Internet-Draft under review: https://datatracker.ietf.org/doc/html/draft-ietf-uuidrev-rfc4122bis-00
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