Parent Table locket while inserting in child table !

The parent table lock with LMODE=3 when an insert command is issued on its child table. An index is also present on the foreign key , but still a table level lock apply on the parent table. Because there is a constraint that requires that the parent exist before the child can be inserted, Oracle locks the parent table to keep the parent record from being deleted while the child record is being inserted. This is a well known issue on Oracle.