Use more efficient queries.

lib/pleroma/activity.ex

@@ -17,11 +17,12 @@ def get_by_ap_id(ap_id) do
 
   def all_by_object_ap_id(ap_id) do
     Repo.all(from activity in Activity,
-      where: fragment("? @> ?", activity.data, ^%{object: %{id: ap_id}}))
+      where: fragment("(?)->'object'->>'id' = ?", activity.data, ^to_string(ap_id)))
   end
 
   def get_create_activity_by_object_ap_id(ap_id) do
     Repo.one(from activity in Activity,
-      where: fragment("? @> ?", activity.data, ^%{type: "Create", object: %{id: ap_id}}))
+      where: fragment("(?)->'object'->>'id' = ?", activity.data, ^to_string(ap_id))
+             and fragment("(?)->>'type' = 'Create'", activity.data))
   end
 end

priv/repo/migrations/20170620133028_add_object_activity_index.exs

+defmodule Pleroma.Repo.Migrations.AddObjectActivityIndex do
+  use Ecto.Migration
+
+  def change do
+    create index(:objects, ["(data->'object'->>'id')", "(data->>'type')"], name: :activities_create_objects_index)
+  end
+end