Explanation
Optimizer Hints Ignored by default in ADW, where honored by default in ATP When migrating data to Autonomous Database, table statistics are gathered automatically during direct path load operations. If direct path load operations are not used, such as with SQL Developer loads, the user can gather statistics manually as needed. When migrating an existing database that uses optimizer in parallel hints, ADB will ignore those by default. Because ADB runs in a highly tuned exadata environment, most database operations should run faster or at least as well as database tune with lots of hints to perform faster. Should hints be required for some reason, they can be explicitly re-enabled.
Autonomous Data Warehouse ignores optimizer hints and PARALLEL hints in SQL statements by default