The initialization parameter PARALLEL_DEGREE_POLICY controls whether automatic degree of parallelism (DOP), parallel statement queuing, and in-memory parallel execution are enabled. This parameter has three possible values:

• MANUAL - Disables automatic DOP, statement queuing and in-memory parallel execution. It reverts the behavior of parallel execution to what it was previous to Oracle Database 11g, Release 2 (11.2), which is the default.

• LIMITED - Enables automatic DOP for some statements but parallel statement queuing and in-memory parallel execution are disabled. Automatic DOP is applied only to statements that access tables or indexes declared explicitly with the PARALLEL clause. Tables and indexes that have a DOP specified use that explicit DOP setting

• AUTO - Enables automatic DOP, parallel statement queuing, and in-memory parallel execution.
  
  
   manual        关闭 AUTO DOP,使用默认的并行参数。
   limited         限制方式，表是使用oracle默认并行度时，oracle会根据资源负载自动评估调整并行度。
   auto            自动方式，auto DOP 针对所有的表。
  
  

  Database VLDB and Partitioning Guide
   Using Parallel Execution