col inst_id for 99 head I# 
col module for a15 trunc
col action for a15 trunc
col event for a40
col blocking_session for 99999 head Blocking|session
col blocking_instance for 99 head BI# 
col blocking_session_status for a10 head Blocking|session|status
col final_blocking_session for 99999 head Final|Blocking|session
col final_blocking_instance for 99 head FBI#
col final_blocking_session_status for a10 head Final|Blocking|session|status

select 
  inst_id,
  sid,
  serial#,
  sql_id,  
  status,
  blocking_session,
  blocking_instance,
  blocking_session_status,
  final_blocking_session,
  final_blocking_instance,
  final_blocking_session_status,
  module,
  action,
  event 
from 
  gv$session 
where 
  action like 'client%' 
order by 
  action asc
/