Insert query optimisation - Oracle
Unless you have a special case, an INSERT with 1.2 million rows should be completed in seconds or minutes at most.

Yes, direct-path insert may significantly reduce execution time.

The above hint in INSERT has no effect without the necessary prerequisites.

Enable Parallel DML Mode


  A DML statement can be parallelized only if you have explicitly
  enabled parallel DML in the session or in the SQL statement. To enable
  this mode in a session, run the following SQL statement:
  
  ALTER SESSION ENABLE PARALLEL DML;
  
  To enable parallel DML mode in a
  specific SQL statement, include the ENABLE_PARALLEL_DML SQL hint. For
  example:
  
  INSERT /*+ ENABLE_PARALLEL_DML */ …
  
  This mode is required because parallel DML and serial DML have different locking, transaction, and
  disk space requirements and parallel DML is disabled for a session by
  default.
  
  When parallel DML is disabled, no DML is executed in parallel even if
  the PARALLEL hint is used.