diff --git a/app/controllers/stats_controller.rb b/app/controllers/stats_controller.rb
index 3e1ec76b..35f7f108 100644
--- a/app/controllers/stats_controller.rb
+++ b/app/controllers/stats_controller.rb
@@ -69,6 +69,8 @@ class StatsController < ApplicationController
     return unless stale? [last_stat, hostnames, interval, normalized_urls, period]
 
     options = { host: hostnames, uri: normalized_paths }
+    # XXX: where_dimensions es más corto pero no aprovecha los índices
+    # de Rollup
     stats = rollup_scope.where_dimensions(**options).multi_series('host|uri', interval: interval).tap do |series|
       series.each do |serie|
         serie[:name] = serie[:dimensions].slice('host', 'uri').values.join.sub('/index.html', '/')