How to enable trace in Oracle

1. Enable trace at instance level

Put the following line in init.ora. It will enable trace for all sessions and the background
processes

sql_trace = TRUE

to disable trace:

sql_trace = FALSE

- or -

to enable tracing without restarting database run the following command in sqlplus

SQLPLUS> ALTER SYSTEM SET trace_enabled = TRUE;

to stop trace run:

SQLPLUS> ALTER SYSTEM SET trace_enabled = FALSE;


2. Enable trace at session level

to start trace:

ALTER SESSION SET sql_trace = TRUE;

to stop trace:

ALTER SESSION SET sql_trace = FALSE;

- or - 

EXECUTE dbms_session.set_sql_trace (TRUE);
EXECUTE dbms_session.set_sql_trace (FALSE);

- or -

EXECUTE dbms_support.start_trace;
EXECUTE dbms_support.stop_trace;


3. Enable trace in another session

Find out SID and SERIAL# from v$session. For example:

SELECT * FROM v$session WHERE osuser = OSUSER;

to start trace:

EXECUTE dbms_support.start_trace_in_session (SID, SERIAL#);

to stop trace:

EXECUTE dbms_support.stop_trace_in_session (SID, SERIAL#);

- or -

EXECUTE dbms_system.set_sql_trace_in_session (SID, SERIAL#, TRUE);
EXECUTE dbms_system.set_sql_trace_in_session (SID, SERIAL#, FALSE);

- or -

-- Oracle 10.1
EXECUTE DBMS_SYSTEM.set_sql_trace_in_session(sid=>SID, serial#=>SERIAL, sql_trace=>TRUE);
EXECUTE DBMS_SYSTEM.set_sql_trace_in_session(sid=>SID, serial#=>SERIAL, sql_trace=>FALSE);