How do I enable "TRACING" of queries and connects ?

Question

As far as I know I can somewhere enable tracing of
all incoming connect (=login session) trials and queries.
How can I turn this tracing on?
Where can I see the tracing log ?

Answer 1

To enable trace for another session currently connected:
EXECUTE SYS.DBMS_SYSTEM.SET_SQL_TRACE_IN_SESSION(<sid>, <serial#>, TRUE );
To disable trace for another session currently connected:
EXECUTE SYS.DBMS_SYSTEM.SET_SQL_TRACE_IN_SESSION(<sid>, <serial#>, FALSE );
To enable trace for you own, current session:
alter session set events '10046 trace name context forever, level 12';
To disable trace for your own current session:
alter session set events '10046 trace name context off';
To see what your current session trace dump file is:
declare
  spid1     VARCHAR2(9);
  tracefile VARCHAR2(80);
  sid_id    VARCHAR2(8);
  udump_loc VARCHAR2(60);
begin
  SELECT spid
    INTO spid1
    FROM v$process a,
         v$session b,
         v$mystat  m
   WHERE a.addr = b.paddr
     AND b.audsid = userenv('SESSIONID')
     AND b.sid    = m.sid
     AND ROWNUM = 1 ;
  SELECT LOWER(instance_name)
    INTO sid_id
    FROM v$instance ;
  SELECT value
    INTO udump_loc
    FROM v$parameter
   WHERE name = 'user_dump_dest' ;
  tracefile:= udump_loc||'/'||sid_id||'_ora_' || spid1 ||'.trc';
  dbms_output.enable(1000000);
  dbms_output.put_line(tracefile);
end;