Tou

Tou, short for Time-Ordered-UUID, is a time-ordered unique identifier scheme. It produces bytes which are compatible with UUIDv4 - the most common UUID format at the moment. While it looks identical to a usual UUIDv4 and will be accepted by all the systems that accept those UUIDs, it has a number of useful properties:

• It starts with the current number of microseconds, packed in network byte order. This means that the UUIDs will sort by byte value in time-ascending order
• It uses 7 bytes of the whole number of microseconds out of 8, giving enough capacity until year 4253
• The rest of the UUID is filled with random bits
• The UUID still has the correct version (4) and variant (1) to be recognized as a UUIDv4

The usage of such UUIDs has some neat properties:

• They sort better in databases using bytes for UUID storage. Iterative SELECTs on large datasets will be much more pleasant.
• They will likely compose into more efficient B-trees in database indexes
• They sort chronologically
• The timestamp can be reconstructed from the UUID, and stays relatively precise
• Any system that accepts UUIDv4 identifiers will also accept Tou identifiers
• ...which means that you do not need, say, Postgres extensions to use UUIDv7

Tou.uuid #=> "061a417b-0e60-4009-9822-72d241ef27d6"

Not much to it, really.

The Tou is laid out as follows (in its byte representation):

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               mus                             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          mus                  |  ver  |  mus  |   random      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var|                       random                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           random                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


mus:
   56-bit big-endian unsigned number of the Unix Epoch timestamp in
   microseconds. Occupies 48 bits (0 through 47 in octets 0-5) and
   4 bits (53 through 57 in octet 6).

ver:
   The 4-bit version field as defined by Section 4.2 of RFC9562,
   set to 0b0100 (4). Occupies bits 48 through 52.

random:
   The 70 bits of pseudorandom data to provide uniqueness as
   per Section 6.9 of RFC9562 and/or an optional counter to guarantee
   additional monotonicity as per Section 6.2 of RFC9562. 
   Occupies bits 49 through 63 and 66 through 127 of
   octets 7 to 15 

var:
   The 2-bit variant field as defined by Section 4.1 of RFC9562,
   set to 0b10. Occupies bits 64 and 65 of octet 8.

Compare this to the UUIDv4 layout:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           random_a                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          random_a             |  ver  |       random_b        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|var|                       random_c                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           random_c                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Add this line to your application's Gemfile:

gem 'tou'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install tou

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/cheddar-me/tou. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Tou project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.