Behaviour for implementing Conflict-free Replicated Data Types (CRDTs).

CRDTs are data structures that can be replicated across multiple nodes, modified independently and concurrently, and merged back together automatically, guaranteeing eventual consistency.

CRDT Properties

All implementations must satisfy these algebraic properties for merge/2:

• Commutativity: merge(a, b) == merge(b, a)
• Associativity: merge(merge(a, b), c) == merge(a, merge(b, c))
• Idempotence: merge(a, a) == a

Example Implementation

defmodule MyApp.GCounter do
  @behaviour Grove.CRDT

  defstruct actor: nil, counts: %{}

  @impl true
  def new(actor), do: %__MODULE__{actor: actor}

  @impl true
  def merge(%__MODULE__{} = a, %__MODULE__{} = b) do
    merged = Map.merge(a.counts, b.counts, fn _k, v1, v2 -> max(v1, v2) end)
    %{a | counts: merged}
  end

  @impl true
  def value(%__MODULE__{counts: counts}) do
    Enum.sum(Map.values(counts))
  end
end