hippware/ex_hash_ring

A fast consistent hash ring implementation in Elixir.

Hash Ring

A pure Elixir consistent hash ring implemention based on the excellent C hash-ring lib by Chris Moos.

The hashring provides fast lookup, but ring creation isn't optimized (though it's not slow). It deliberately does not provide encapsulation within a GenServer and leaves that up to the user. At Discord we found using a GenServer for such frequently accessed data proved to be overwhelming so we rewrote the hash ring in pure Elixir and paired it with FastGlobal to allow the calling process to use it's CPU time to interact with the hash ring and therefore avoiding overloading a central GenServer.

Usage

Add it to mix.exs.

defp deps do
  [{:ex_hash_ring, "~> 3.0"}]
end

Create a new HashRing.

alias ExHashRing.HashRing

ring = HashRing.new
{:ok, ring} = HashRing.add_node(ring, "a")
{:ok, ring} = HashRing.add_node(ring, "b")

Find the node for a key.

"a" = HashRing.find_node(ring, "key1")
"b" = HashRing.find_node(ring, "key3")

Additionally, you can also use ExHashRing.HashRing.ETS, which holds the ring in an ETS table for fast access, if you need the ring across multiple processes.

{:ok, pid} = HashRing.ETS.start_link(TheRing)
{:ok, _nodes} = HashRing.ETS.add_node(pid, "a")
{:ok, _nodes} = HashRing.ETS.add_node(pid, "b")

And then find a node for a key, using the ETS name provided:

"a" = HashRing.ETS.find_node(TheRing, "key1")
"b" = HashRing.ETS.find_node(TheRing, "key3")

License

Hash Ring is released under the MIT License. Check LICENSE file for more information.