Oracle 查询阻塞

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如果你的 SQL 或系统突然 hang 了，很有可能是因为一个 session 阻塞了另一个 session，如何查询是否发生阻塞了呢？看看下面的 SQL吧。

select 
	blocksession.sid        as block_session_sid,
	blocksession.serial#    as block_session_serial#,
	blocksession.username   as block_session_username,
	blocksession.osuser     as block_session_osuser,
	blocksession.machine    as block_session_machine,
	blocksession.status     as block_session_status,
	blockobject.object_name as blocked_table,
	waitsession.sid         as wait_session_sid,
	waitsession.serial#     as wait_session_serial#,
	waitsession.username    as wait_session_username,
	waitsession.osuser      as wait_session_osuser,
	waitsession.machine     as wait_session_machine,
	waitsession.status      as wait_session_status
from 
	v$lock          blocklock,
	v$lock          waitlock,
	v$session       blocksession,
	v$session       waitsession,
	v$locked_object lockedobject,
	dba_objects     blockobject
where 
	blocklock.block    = 1
	and blocklock.sid != waitlock.sid
	and blocklock.id1 = waitlock.id1
	and blocklock.id2 = waitlock.id2
	and blocklock.sid = blocksession.sid
	and waitlock.sid  = waitsession.sid
	and lockedobject.session_id = blocksession.sid
	and lockedobject.object_id  = blockobject.object_id;

如果上面的语句返回了结果，表明发生了阻塞，这个时候你可以把使用 blocksession 的程序停掉。如果还是不能解决问题，那只能让 DBA 帮你把 blocksession kill 掉，如何 kill 呢？ 试一试下面的语句吧。

ALTER SYSTEM KILL SESSION '<block_session_sid>,<block_session_serial#>';
ALTER SYSTEM KILL SESSION '113,55609';

如果没有发生阻塞，系统就是很慢，该怎么办呢？在"Oracle 查询耗时 SQL"找答案吧。

--更多参见：Oracle SQL 优化精萃

-- 声明：转载请注明出处

-- Last edited on 2015-08-28

-- Created by ShangBo on 2015-08-07

-- End