How to trace

--Instance-level trace

alter system|session set sql_trace=true;

--session-level SQL tracing
select sid,serial# from v$session where username='ABC' ;
execute dbms_monitor.session_trace_enable(session_id=>123, serial_num=>123);
execute dbms_monitor.session_trace_disable(session_id=>123, serial_num=>123);

Tracing with database control
--The DBMS_MONITOR packages has procedures that will let you enable tracing at these levels:
*session level
*Module level
*Client ID level
*Service Level
*Action