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What is a UUID? and the difference between versions

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Posted on 2024-10-18 16:31:13 | | |
Requirements: Find a UUID generator and find that UUIDs are also version-differentiated.

What is a UUID?

The Universally Unique Identifier (UUID) is a 128-digit identifier used to uniquely identify a piece of information in the system.

According to the standard (RFC 4122 (opens new window)), UUIDs are generated without relying on external services and are unique (note: the probability of duplication is almost zero).

UUIDs are made up of 32 numbers in hexadecimal, so the theoretical total is 16^32, and even if one trillion are generated per nanosecond, it will take ten billion years to use up all UUIDs.

In its canonical text representation, the UUID's 16 8-bit bytes are represented as 32 hexadecimal numbers, separated by the hyphen '-' displayed in five groups in the form "8-4-4-4-12" for a total of 36 characters (32 hexadecimal numbers and 4 hyphens).

For example:

123e4567-e89b-12d3-a456-426655440000
xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

UUID version

  • v1- Version 1 UUID uses timestamps and monotonic counters.
  • v3 - Version 3 UUID based on MD5 hashes of some data.
  • v4 - Version 4 UUID with random data.
  • v5- Version 5 UUID based on SHA1 hashes of some data.
  • v6- Version 6 UUID uses timestamps and monotonic counters.
  • v7 - Version 7 UUID with Unix timestamps.
  • v8 - Version 8 UUID with user-defined data.


Which UUID version should I use?

If you only want to generate unique identifiers, consider version 4 (v4) UUIDs. If you want to use UUIDs as database keys or need to sort them, consider version 7 (v7) UUIDs. Other versions should generally be avoided unless there is an existing demand.

Some UUID versions supersede others. Version 6 is better than version 1, and version 5 is better than version 3.

UUID and GUID difference

Standards and implementations: UUID is an open standard, while GUID is a specific implementation of the UUID standard by Microsoft.

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