What can cause intermittent ORA-12519 (TNS: no appropriate handler found) errors...

Oracle listener state blocked...

ORA-12519, TNS:no appropriate service handler found while inserting into Oracle Database with X thre...

Oracle 12519 : Issues while running integration test suite...

What causes an ORA-12519 to be thrown even though the Oracle trace file for the event shows an ORA-0...

getting java.sql.SQLException: Closed Connection when accessing large resultset...

Why do I get this Oracle connections error? ORA-12519, TNS:no appropriate service handler found...