IMHO, if you want perfect uniqueness, you have to sacrifice randomness. I’ve written a module for myself, it generates alphanumeric ID’s based on a 48-bit timestamp, a 32-bit node name hash code, and a 16-bit sequence number.
defmodule CUID do
@moduledoc """
CUID is for **Cluster-Unique ID**. It's shorter than UUID, case sensitive, and URL-safe.
The generated ID is guaranteed to be unique among the BEAM cluster
if there are no more than 65536 nodes in the cluster,
and the request rate is lower than 256 req/(node * millisec).
## Examples
iex> CUID.start_link(CUID)
iex> CUID.gen(CUID)
"AWAAtXL1doYA"
"""
use Agent
use Bitwise
@doc """
Start a `CUID` process linked to the current process.
"""
def start_link(name) do
case Agent.start_link(fn -> 0 end, name: name) do
{:error, {:already_started, _}} -> :ignore
other -> other
end
end
@doc """
Generate a CUID.
"""
def gen(server) do
now = System.os_time(:millisecond) # 48 bits
node_name_hash = Node.self() |> Atom.to_charlist() |> Enum.reduce(0, fn(char, hash) ->
((hash <<< 5) - hash + char) &&& 0xFFFF
end) # 32 bits
n = Agent.get_and_update(server, fn n -> {n, (n + 1) &&& 0xFF} end) # 16 bits
<<now::48, node_name_hash::16, n::8>> |> Base.url_encode64(padding: false)
end
end
