Add count index for local users.

priv/repo/migrations/20171130135819_add_local_index_to_user.exs

@@ -0,0 +1,7 @@
+defmodule Pleroma.Repo.Migrations.AddLocalIndexToUser do
+  use Ecto.Migration
+
+  def change do
+    create index(:users, [:local])
+  end
+end