An INSERT SELECT statement parallelizes its INSERT and SELECT operations independently, except for the DOP.
You can specify a parallel hint after the INSERT keyword in an INSERT SELECT statement. Because the tables being queried are usually different than the table being inserted into, the hint enables you to specify parallel directives specifically for the insert operation.
You have the following ways to specify parallel directives for an INSERT SELECT statement (if PARALLEL DML mode is enabled):
SELECT parallel hints specified at the statement
Parallel clauses specified in the definition of tables being selected
INSERT parallel hint specified at the statement
Parallel clause specified in the definition of tables being inserted into
You can use the ALTER SESSION FORCE PARALLEL DML statement to override parallel clauses for subsequent INSERT operations in a session. Parallel hints in insert operations override the ALTER SESSION FORCE PARALLEL DML statement.