可以查到锁锁源头

select *

  from (select a.sid,

               a.sql_id,

               a.event,

               a.status,

               connect_by_isleaf as isleaf,

               sys_connect_by_path(SID, '<-') tree,

               level as tree_level

          from v$session a

         start with a.blocking_session is not null

        connect by nocycle a.sid = prior a.blocking_session)

 where isleaf = 1

 order by tree_level asc;

正在发生的话，直接查数据库的阻塞链表
已经发生事后排查的话可以通过v$active_session_history进行排查