lib/active_support/notifications.rb in activesupport-3.2.0.rc2 vs lib/active_support/notifications.rb in activesupport-3.2.0

@@ -66,9 +66,13 @@
   # == Temporary Subscriptions
   #
   # Sometimes you do not want to subscribe to an event for the entire life of
   # the application. There are two ways to unsubscribe.
   #
+  # WARNING: The instrumentation framework is designed for long-running subscribers,
+  # use this feature sparingly because it wipes some internal caches and that has
+  # a negative impact on performance.
+  #
   # === Subscribe While a Block Runs
   #
   # You can subscribe to some event temporarily while some block runs. For
   # example, in
   #