The following rule determines whether the UPDATE, MERGE, or DELETE operation should be executed in parallel:
The UPDATE or DELETE operation is parallelized if and only if at least one of the following is true:
The table being updated or deleted has a PARALLEL specification.
The PARALLEL hint is specified in the DML statement.
An ALTER SESSION FORCE PARALLEL DML statement has been issued previously during the session.
If the statement contains subqueries or updatable views, then they may have their own separate parallel hints or clauses. However, these parallel directives do not affect the decision to parallelize the UPDATE, MERGE, or DELETE operations.
The parallel hint or clause on the tables is used by both the query and the UPDATE, MERGE, DELETE portions to determine parallelism, the decision to parallelize the UPDATE, MERGE, or DELETE portion is independent of the query portion, and vice versa.