一 模拟锁阻塞

#阻塞1

一个会话正在往一个大表写入大量数据的时候，另一个会话加字段：

#会话1

#会话2

会话2被阻塞了。

#阻塞2

模拟一个会话update一条记录，没提交。

另一个会话也update这一条记录：

会话2被阻塞了。

二 简单查看阻塞链

select *
  from (select a.inst_id,a.sid, a.serial#,
               a.sql_id,
               a.event,
               a.status,
               connect_by_isleaf as isleaf,
               sys_connect_by_path(SID, '<-') tree,
               level as tree_level
          from gv$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;

输出示例：

TREE这里可以看到阻塞链（从右往左看），这里是：

978阻塞了729；

372阻塞了616。

三 查看具体谁阻塞了谁

SELECT DISTINCT s1.inst_id as blocking_inst_id,s1.username as blocking_username,s1.machine as blocking_machine,s1.sid as blocking_sid,s1.serial# as blocking_serial#,c1.sql_text as blocking_sql_text,s1.status as blocking_staus,s1.event as blocking_event,
s2.inst_id as waiting_inst_id,s2.username as waiting_username,s2.machine waiting_machine,s2.sid as waiting_sid,s2.serial# as waiting_serial#,c2.sql_text as waiting_sql_text,s2.status as blocking_staus,s2.event as waiting_event
  FROM gv$lock l1,
       gv$session s1,
       gv$lock l2,
       gv$session s2,
       gv$sqlarea c1,
       gv$sqlarea c2,
       gv$process b1,
       gv$process b2
 WHERE     s1.sid = l1.sid
       AND s2.sid = l2.sid
       AND s1.inst_id = l1.inst_id
       AND s2.inst_id = l2.inst_id
       AND s1.paddr = b1.addr
       AND s2.paddr = b2.addr
       AND c1.SQL_ID=s1.PREV_SQL_ID       
       AND s2.sql_hash_value = c2.hash_value
       AND l1.block > 0
       AND l2.request > 0
       AND l1.id1 = l2.id1
       AND l1.id2 = l2.id2
UNION
SELECT DISTINCT s1.inst_id as blocking_inst_id,s1.username as blocking_username,s1.machine as blocking_machine,s1.sid as blocking_sid,s1.serial# as blocking_serial#,c1.sql_text as blocking_sql_text,s1.status as blocking_staus,s1.event as blocking_event,
s2.inst_id as waiting_inst_id,s2.username as waiting_username,s2.machine waiting_machine,s2.sid as waiting_sid,s2.serial# as waiting_serial#,c2.sql_text as waiting_sql_text,s2.status as blocking_staus,s2.event as waiting_event
  FROM gv$lock l1,
       gv$session s1,
       gv$lock l2,
       gv$session s2,
       gv$sqlarea c1,
       gv$sqlarea c2,
       gv$process b1,
       gv$process b2
 WHERE     s1.sid = l1.sid
       AND s2.sid = l2.sid
       AND s1.inst_id = l1.inst_id
       AND s2.inst_id = l2.inst_id
       AND s1.paddr = b1.addr
       AND s2.paddr = b2.addr
       AND c1.hash_value=s1.sql_hash_value
       AND c1.address=s1.sql_address
       AND s2.sql_hash_value = c2.hash_value
       AND l1.block > 0
       AND l2.request > 0
       AND l1.id1 = l2.id1
       AND l1.id2 = l2.id2

#备注

union前的sql可以查看源端执行过的sql（在一个事务里执行了，但是还没提交）。

union后的sql可以查看当前源端正在执行的sql。

一次性展示不全，这里分三个截图展示：

在每条记录里可以看到是谁阻塞了谁。

但是假如源端执行了这个事务后，又执行了其他事务，这时候查看源端阻塞sql就不准确了。

示例：

源端执行了一个事务，然后有执行了一个其他的sql，这时查看源端的阻塞sql是这样的：

这时结果是不准确的。