issue #75: improve cache replicas selection logic

1 node        -> 1 replica
2, 3, 4 nodes -> 2 replicas
5 nodes       -> 3 replicas
6, 7 nodes    -> 4 replicas
...

Signed-off-by: Matteo Cafasso <[email protected]>

Author: noxdafox

lib/rabbitmq_message_deduplication/cache.ex

@@ -219,10 +219,15 @@ defmodule RabbitMQMessageDeduplication.Cache do
   end
 
   # List the nodes on which to create the cache replicas.
-  # Distributed caches are replicated on two-third of the cluster nodes.
+  # Distributed caches are replicated on two-thirds of the cluster nodes.
   defp cache_replicas(_distributed = true) do
     nodes = [Node.self() | Node.list()]
-    nodes |> Enum.split(round((length(nodes) * 2) / 3)) |> elem(0)
+
+    if length(nodes) > 2 do
+      nodes |> Enum.split(floor((length(nodes) * 2) / 3)) |> elem(0)
+    else
+      nodes
+    end
   end
 
   # List the nodes on which to create the cache replicas.