Index users by ap_id.

priv/repo/migrations/20170506222027_add_unique_index_to_apid.exs

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