There are several initialization parameters that control automatic DOP:
PARALLEL_DEGREE_LIMIT. For information about setting the
PARALLEL_DEGREE_POLICY initialization parameter, refer to "Controlling Automatic DOP_ Parallel Statement Queuing_ and In-Memory Parallel Execution".
PARALLEL_MIN_TIME_THRESHOLD initialization parameter specifies the minimum execution time a statement should have before the statement is considered for automatic DOP. The optimizer first calculates a serial execution plan for the SQL statement; if the estimated execution elapsed time is greater than the value of
PARALLEL_MIN_TIME_THRESHOLD, the statement becomes a candidate for automatic DOP.
PARALLEL_DEGREE_LIMIT initialization parameter specifies the maximum DOP for automatic DOP systemwide. For a more fine grained control of the maximum DOP, you can use Database Resource Manager.
For additional information, refer to "Automatic Degree of Parallelism" and "Controlling Automatic DOP_ Parallel Statement Queuing_ and In-Memory Parallel Execution".
There are also other techniques that you can use to control parallelism. For additional information, refer to "Miscellaneous Parallel Execution Tuning Tips".