Enabling Trace in Oracle

Tracing a session is a imporatant phase of a problem analysis for a query,job in Oracle.There are various methods of enabling trace for sessions.Following are a few methods for enabling trace.
To check if any trace is enabled in the current database, the following query can be used:
select * from DBA_ENABLED_TRACES ;

1. Enable trace at instance level
Start trace:
SQLPLUS> ALTER SYSTEM SET sql_trace = TRUE;
Stop trace:
SQLPLUS> ALTER SYSTEM SET sql_trace = FALSE;

2. Enable trace for the current session
Start trace:
ALTER SESSION SET sql_trace = TRUE; (or)EXECUTE dbms_session.set_sql_trace (TRUE); (or)EXECUTE dbms_support.start_trace;Stop trace:
ALTER SESSION SET sql_trace = FALSE; (or)EXECUTE dbms_session.set_sql_trace (FALSE); (or)EXECUTE dbms_support.stop_trace;

3. Enable trace in another session
Find out SID and SERIAL# from v$session. For example:
Start trace:
EXECUTE DBMS_MONITOR..start_trace_in_session (SID, SERIAL#);
With Waits and Binds
EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(SID, SERIAL#, waits=>TRUE);
With Waits
EXECUTE DBMS_MONITOR.SESSION_TRACE_ENABLE(SID, SERIAL#, waits=>TRUE, binds=>TRUE);

Stop trace:
EXECUTE dbms_support.stop_trace_in_session (SID, SERIAL#);