Make user timelines faster for users with few statuses.

priv/repo/migrations/20170701142005_add_actor_index_to_activity.exs

@@ -0,0 +1,7 @@
+defmodule Pleroma.Repo.Migrations.AddActorIndexToActivity do
+  use Ecto.Migration
+
+  def change do
+    create index(:activities, ["(data->>'actor')", "inserted_at desc"], name: :activities_actor_index)
+  end
+end