Oracle中锁（lock）的用法

数据库锁介绍： https://www.jb51.net/article/248863.htm

一、查询oracle锁定的表：

1、锁相关表

• SELECT * FROM v$lock; 
  列：ADDR:锁定状态对象地址;KADDR:锁地址;SID :会话id;ID1:锁标识符#1;ID2:锁标识符#2;LMODE:会话持有的锁模式（0~6）;REQUEST:进程请求的锁模式（0~6）; 
  CTIME:当前模式的时间;BLOCK:为1代表阻碍者，表示正在阻碍其它会话;
• SELECT * FROM v$locked_object;
• SELECT * FROM v$session;
• SELECT * FROM v$session_wait;
• SELECT * FROM v$sqlarea;
• SELECT * FROM v$process ;
• SELECT * FROM all_objects

2、常用语句

1、查出锁定object的session的信息以及被锁定的object名

SELECT l.session_id sid, s.serial#, l.locked_mode, l.oracle_username, l.os_user_name, s.machine, s.terminal, o.object_name, s.logon_time
FROM v$locked_object l, all_objects o, v$session s
WHERE l.object_id = o.object_id
AND l.session_id = s.sid
ORDER BY sid, s.serial#;

2、查出锁定表的session的sid, serial#,os_user_name, machine name, terminal和执行的语句，比上面那段多出sql_text和action

SELECT l.session_id sid, s.serial#, l.locked_mode, l.oracle_username, s.user#, l.os_user_name, s.machine, s.terminal, a.sql_text, a.action
FROM v$sqlarea a, v$session s, v$locked_object l
WHERE l.session_id = s.sid
AND s.prev_sql_addr = a.address
ORDER BY sid, s.serial#;

3、查出锁定表的sid, serial#,os_user_name, machine_name, terminal，锁的type,mode

SELECT s.sid, s.serial#, s.username, s.schemaname, s.osuser, s.process, s.machine, s.terminal, s.logon_time, l.TYPE
FROM v$session s, v$lock l
WHERE s.sid = l.sid
AND s.username IS NOT NULL
ORDER BY sid;

4、这个语句将查找到数据库中所有的DML语句产生的锁，还可以发现，任何DML语句其实产生了两个锁，一个是表锁，一个是行锁。

SELECT /*+ rule */
 s.username, DECODE(l.TYPE, 'TM', 'TABLE LOCK', 'TX', 'ROW LOCK', NULL) LOCK_LEVEL, o.owner, o.object_name, o.object_type, s.sid, s.serial#, s.terminal, s.machine, s.program, s.osuser
FROM v$session s, v$lock l, dba_objects o
WHERE l.sid = s.sid
AND l.id1 = o.object_id(+)
AND s.username IS NOT NULL;

5、如果发生了锁等待，我们可能更想知道是谁锁了表而引起谁的等待,以下的语句可以查询到谁锁了表，而谁在等待。

以下查询结果是一个树状结构，如果有子节点，则表示有等待发生。如果想知道锁用了哪个回滚段，还可以关联到V$rollname，其中xidusn就是回滚段的USN

SELECT LPAD(' ', DECODE(l.xidusn, 0, 3, 0)) || l.oracle_username user_name, o.owner, o.object_name, o.object_type, s.sid, s.serial#
FROM v$locked_object l, dba_objects o, v$session s
WHERE l.object_id = o.object_id
AND l.session_id = s.sid
ORDER BY o.object_id, xidusn DESC

3、kill session语句：

alter system kill session 'sid,serial#';

alter system kill session'494,7355';

二、一个有用查找脚本：

1、找到某表的锁 所属的sid，alter system kill session 'sid,serial#';即可

select v$lock.sid, decode(v$lock.type, 'MR', 'Media Recovery', 'RT', 'Redo Thread', 'UN', 'User Name', 'TX', 'Transaction', 'TM', 'DML', 'UL', 'PL/SQL User Lock', 'DX', 'Distributed Xaction', 'CF', 'Control File', 'IS', 'Instance State', 'FS', 'File Set', 'IR', 'Instance Recovery', 'ST', 'Disk Space Transaction', 'TS', 'Temp Segment', 'IV', 'Library Cache Invalida-tion', 'LS', 'Log Start or Switch', 'RW', 'Row Wait', 'SQ', 'Sequence Number', 'TE', 'Extend Table', 'TT', 'Temp Table', 'Unknown') LockType, rtrim(owner) || '.' ||
        object_name object_name, decode(lmode, 0, 'None', 1, 'Null', 2, 'Row-S', 3, 'Row-X', 4, 'Share', 5, 'S/Row-X', 6, 'Exclusive', 'Unknown') LockMode, decode(request, 0, 'None', 1, 'Null', 2, 'Row-S', 3, 'Row-X', 4, 'Share', 5, 'S/Row-X', 6, 'Exclusive', 'Unknown') RequestMode, ctime, block b
from v$lock, all_objects
where sid > 6
and v$lock.id1 = all_objects.object_id;

2、查出被lock 的对象，然后 alter system kill session 'sid,serial#';

select object_id, session_id, serial#, oracle_username, os_user_name, s.process
from v$locked_object a, v$session s
where a.session_id = s.sid;

三、LOCK TABLE

1、语法：

LOCK   TABLE   table_1   [,table_2,   ...,   table_n]   IN   lock_mode   MODE
  NOWAIT

2、变量：

table_1,...,table_n: 一系列你想通过使用LOCK TABLE语句锁住的数据库表。

lock_mode: 对于某一数据库表你要设定的锁定模式。你可以从如下的锁定模式中任选一个。

• EXCLUSIVE
• SHARE ROW EXCLUSIVE
• SHARE
• SHARE UPDATE
• ROW SHARE
• ROW EXCLUSIVE

NOWAIT: Oracle will not wait to lock the given Table(s), if the Table(s) is(are) not available

3、例子：

LOCK   TABLE   loan     IN   SHARE   MODE   ;
LOCK   TABLE   region   IN   EXCLUSIVE   MODE   NOWAIT;
LOCK   TABLE   acct     IN   SHARE   UPDATE   MODE;
LOCK   TABLE   bank     IN   ROW   EXCLUSIVE   MODE   NOWAIT;
LOCK   TABLE   user     IN   SHARE   ROW   EXCLUSIVE   MODE;
LOCK   TABLE   branch   IN   ROW   SHARE   MODE   NOWAIT;
commit

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