Extract host from ap_id, add index

priv/repo/migrations/20180606173637_create_apid_host_extraction_index.exs

@@ -0,0 +1,8 @@
+defmodule Pleroma.Repo.Migrations.CreateApidHostExtractionIndex do
+  use Ecto.Migration
+  @disable_ddl_transaction true
+
+  def change do
+    create index(:activities, ["(split_part(actor, '/', 3))"], concurrently: true, name: :activities_hosts)
+  end
+end