Separate Registry pool size configuration

lib/phoenix/pubsub.ex

@@ -164,6 +164,10 @@ defmodule Phoenix.PubSub do
     * `:adapter` - the adapter to use (defaults to `Phoenix.PubSub.PG2`)
     * `:pool_size` - number of pubsub partitions to launch
       (defaults to one partition for every 4 cores)
+    * `:registry_size` - number of `Registry` partitions to launch
+      (defaults to `:pool_size`). This controls the number of Registry partitions
+      used for storing subscriptions and can be tuned independently from `:pool_size`
+      for better performance characteristics.
     * `:broadcast_pool_size` - number of pubsub partitions used for broadcasting messages
       (defaults to `:pool_size`). This option is used during pool size migrations to ensure
       no messages are lost. See the "Safe Pool Size Migration" section in the module documentation.

lib/phoenix/pubsub/supervisor.ex

@@ -22,7 +22,7 @@ defmodule Phoenix.PubSub.Supervisor do
     adapter_name = Module.concat(name, "Adapter")
 
     partitions =
-      opts[:pool_size] ||
+      opts[:registry_size] || opts[:pool_size] ||
         System.schedulers_online() |> Kernel./(4) |> Float.ceil() |> trunc()
 
     registry = [

test/shared/pubsub_test.exs

@@ -41,15 +41,17 @@ defmodule Phoenix.PubSubTest do
 
   setup config do
     size = config[:pool_size] || 1
+    registry_size = config[:registry_size] || config[:registry_pool_size] || config[:pool_size] ||  1
     {adapter, adapter_opts} = Application.get_env(:phoenix_pubsub, :test_adapter)
-    adapter_opts = [adapter: adapter, name: config.test, pool_size: size] ++ adapter_opts
+    adapter_opts = [adapter: adapter, name: config.test, pool_size: size, registry_size: registry_size] ++ adapter_opts
     start_supervised!({Phoenix.PubSub, adapter_opts})
 
     opts = %{
       pubsub: config.test,
       topic: to_string(config.test),
       pool_size: size,
-      node: Phoenix.PubSub.node_name(config.test)
+      node: Phoenix.PubSub.node_name(config.test),
+      adapter_name: Module.concat(config.test, "Adapter")
     }
 
     {:ok, opts}
@@ -174,4 +176,23 @@ defmodule Phoenix.PubSubTest do
       assert_receive {:custom, :special, :none, :direct}
     end
   end
+
+  @tag pool_size: 4
+  @tag registry_size: 2
+  test "PubSub pool size can be configured separately from the Registry partitions",
+       config do
+    assert {:duplicate, 2, _} = :ets.lookup_element(config.pubsub, -2, 2)
+
+    assert :persistent_term.get(config.adapter_name) ==
+      {config.adapter_name, :"#{config.adapter_name}_2", :"#{config.adapter_name}_3", :"#{config.adapter_name}_4"}
+  end
+
+  @tag pool_size: 3
+  test "Registry partitions are configured with the same pool size as PubSub if not specified",
+       config do
+    assert {:duplicate, 3, _} = :ets.lookup_element(config.pubsub, -2, 2)
+
+    assert :persistent_term.get(config.adapter_name) ==
+      {config.adapter_name, :"#{config.adapter_name}_2", :"#{config.adapter_name}_3"}
+  end
 end