diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index <HASH>..<HASH> 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -763,6 +763,8 @@ module ActiveRecord
       #   An empty array is returned if none are found.
       # [collection<<(object, ...)]
       #   Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
+      #   Note that this operation instantly fires update sql without waiting for the save or update call on the 
+      #   parent object.
       # [collection.delete(object, ...)]
       #   Removes one or more objects from the collection by setting their foreign keys to +NULL+.
       #   Objects will be in addition destroyed if they're associated with <tt>:dependent => :destroy</tt>,
@@ -1186,6 +1188,8 @@ module ActiveRecord
       # [collection<<(object, ...)]
       #   Adds one or more objects to the collection by creating associations in the join table
       #   (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
+      #   Note that this operation instantly fires update sql without waiting for the save or update call on the 
+      #   parent object.
       # [collection.delete(object, ...)]
       #   Removes one or more objects from the collection by removing their associations from the join table.
       #   This does not destroy the objects.
added more info about << operation in associations