ksuid is sortable uuid

I’ll throw ecto_ulid out there too. ULID is a pretty nice ID type (and while I realize this post is about IDs in Cassandra) but its lack of support in Postgres turned into a PITA. I was storing it as a :binary_id since it’s a 128bit integer but querying by the human-readable format was impossible; I had to convert it manually and that got old.

Anyway, here’s a good write-up of the differences between ULID & KSUID. Both are likely great options for your use case.

A cursory look through Xandra’s documentation and source code shows that Xandra does not (yet?) expose any way to generate timeuuid’s in Elixir (but only encoding/decoding values genereated from within Cassandra).

I did find another library called ‘Cassandra’ which has not seen very much usage and has not been updated in a couple of years, but it does contain an internal (undocumented) module called Cassandra.UUID which seems to generate UUIDs in the desired format.

Looking at that module in a bit more detail, it seems like the actual work is offloaded to elixir_uuid (which is stable and widely used), and that Cassandra’s timeuuids are nothing else than ‘v1’ UUIDs.

So using elixir_uuid is probably the best approach .

Snowflake IDs, GitHub - pggalaviz/exnowflake: A decentralized, unique, time based ID generator. .

Docs:

https://hexdocs.pm/exnowflake/readme.html

I just ported the Cassandra::Uuid::Generator code from the official Cassandra Ruby gem:

defmodule TimeUuid do
  use Bitwise, only_operators: true

  @gregorian_offset 122192928000000000

  def new(date_time, jitter \\ nil) do
    jitter = jitter || :rand.uniform(65536)
    clock_id = :rand.uniform(65536)
    node_id = generate_node_id()
    usecs = DateTime.to_unix(date_time, :microsecond) + jitter

    t = @gregorian_offset + usecs * 10
    time_hi  = t &&& 0x0fff000000000000
    time_mid = t &&& 0x0000ffff00000000
    time_low = t &&& 0x00000000ffffffff
    version = 1
    clock_id = clock_id &&& 0x3fff
    node_id = node_id &&& 0xffffffffffff
    variant = 0x8000

    n = (time_low <<< 96) ||| (time_mid <<< 48) ||| (time_hi <<< 16)
    n = n ||| (version <<< 76)
    n = n ||| ((clock_id ||| variant) <<< 48)
    n = n ||| node_id

    <<n::integer-size(128)>>
    |> UUID.binary_to_string!()
  end

  def generate_node_id do
    :math.pow(2, 47)
    |> trunc()
    |> :rand.uniform()
    |> Bitwise.bor(0x010000000000)
  end

end