Creating an Index Online
You can create and rebuild indexes online. This enables you to update base tables at the same time you are building or rebuilding indexes on that table. You can perform DML operations while the index build is taking place, but DDL operations are not allowed. Parallel execution is not supported when creating or rebuilding an index online.
The following statements illustrate online index build operations:
CREATE INDEX emp_name ON emp (mgr, emp1, emp2, emp3) ONLINE;