show parameter audit_trail;
select value from v$parameter where name like'audit_trail';

alter system set audit_trail="true" scope=spfile;
-- shutdown immediate 
-- startup

audit index by scott whenever successful;
grant index on hr.jobs to scott;

-- scott
create index job_title_idx on hr.jobs(job_title);

select username, to_char(timestamp, 'MM/DD/YY HH24:MI') Timestamp, 
obj_name, action_name, sql_text from dba_audit_trail where username ='SCOTT';

noaudit index by scott;