Just a quick heads-up for anyone who likes to play around with the Keep and Recycle caches.
In 11g Oracle introduced the option for serial direct path reads for tablescans on tables that was sufficiently large – which meant more than the small_table_threshold – provided the table wasn’t already sufficient well cached. (The rules mean that the choice of mechanism can appear to be a little random in the production environment for tables that are near the threshold size – but if you try testing by doing “alter system flush buffer_cache” you find that you always get direct path reads in testing.)