Oracle query plan analysis

1. explain plan

for select...

select plan_table_output from table(dbms_xplan.display(format =>'ALL'))  

2. autotrace via sqlplus

set autotrace traceonly;

3. hint gather_plan_statistics

select /*+ GATHER_PLAN_STATISTICS */  /*  xxx001*/

select sql_id, child_number

  from v$sql  

where sql_text like '%xxx001%';

select * from table(dbms_xplan.display_cursor( '50t9x60v9tsk3', 0, 'ALLSTATS LAST'))