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TM表锁各种mode的实验及2

时间:2021-07-01 10:21:17 帮助过:42人阅读

TM 表锁,发生在insert,update,delete以及select for update操作时,目的是保证操作能够正常进行,并且阻止其它人对表执行DDL操作。 TM锁几种模式的互斥关系图: 在巡检期间,检查如果发现有相关的session_wait锁,可按以下步骤查找相应的锁 1. 使用V$LOCK找


TM 表锁,发生在insert,update,delete以及select for update操作时,目的是保证操作能够正常进行,并且阻止其它人对表执行DDL操作。

TM锁几种模式的互斥关系图:

在巡检期间,检查如果发现有相关的session_wait锁,可按以下步骤查找相应的锁

1. 使用V$LOCK找出session持有的锁。

2. 使用V$SESSION找出持有锁或等待锁的session执行的sql语句。

3. 使用V$SESSION_WAIT找出什么原因导致session持有锁堵塞。

4. 使用V$SESSION获取关于持有锁的程序和用户的更多信息。

V$LOCK中的常用列

SID:表示持有锁的会话信息。

TYPE:表示锁的类型。值包括TM和TX等。

LMODE:表示会话等待的锁模式的信息。用数字0-6表示,和表1相对应。

REQUEST:表示session请求的锁模式的信息。

ID1,ID2:表示锁的对象标识。

例如:首先查出当前TM','TX等待事件的等待会话

BYS@ bys3>select a.sid,a.kaddr,a.addr,a.type,a.id1,a.id2,a.lmode,a.request,a.block from v$lock a where a.type in('TM','TX') order by 1,2;
SID KADDR ADDR TY ID1 ID2 LMODE REQUEST BLOCK
---------- -------- -------- -- ---------- ---------- ---------- ---------- ----------
1 B693D590 B693D560 TM 22326 0 0 3 0
44 B693D590 B693D560 TM 22326 0 5 0
BYS@ bys3>select sql_id from v$session where sid=1; 通过上一步会话SID,查出1号会话当前在等待的语句
SQL_ID
-------------
01mv5v746cfbq
BYS@ bys3>select * from v$sqltext where sql_id='01mv5v746cfbq'; --通过上一步查出SQL_SID,查出SQL_TEXT
ADDRESS HASH_VALUE SQL_ID COMMAND_TYPE PIECE SQL_TEXT
-------- ---------- ------------- ------------ ---------- ------------------------------
25DDD5FC 3362142582 01mv5v746cfbq 6 0 update test set status=8899

用一条语句来查询是:select a.*,b.sid,b.username from v$sqltext a,v$session b,v$lock c where a.sql_id=b.sql_id and b.sid=c.sid and c.type in('TM','TX');

详见:v$session/v$process视图涉及的相关会话信息的查询

1.环境准备:--有些实验数据是后来补充的,可能不太一致。
BYS@ bys001>select distinct sid from v$mystat;
SID
----------
19
BYS@ bys001>select * from test;
no rows selected
BYS@ bys001>insert into test values(1);
1 row created.
BYS@ bys001>commit;
Commit complete.
BYS@ bys001>select * from test;
A
----------
1
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;

no rows selected

TM锁1号锁实验:

create table order_info(customerid number);

CREATE OR REPLACE PROCEDURE kzcz214001 (cust_id in NUMBER)
AS
BEGIN
insert into order_info values(cust_id);
commit;
END;
/
col owner for a10
col name for a10
col type for a10
select SESSION_ID sid,OWNER,NAME,Type,MODE_HELD held,MODE_REQUESTED request from dba_ddl_locks WHERE NAME='KZCZ214001';
这一句查询dba_ddl_locks表,如果手工建库,dba_ddl_locks表可能不存在,需要SYS用户运行脚本去创建:?/rdbms/admin/catblock.sql
exec kzcz214001(1);
BYS@ bys3>select SESSION_ID sid,OWNER,NAME,Type,MODE_HELD held,MODE_REQUESTED request from dba_ddl_locks WHERE NAME='KZCZ214001';
SID OWNER NAME TYPE HELD REQUEST
---------- ---------- ---------- ---------- --------- ---------
1 BYS KZCZ214001 Table/Proc Null None
edure/Type
BYS@ bys3>select status from dba_objects where object_name='KZCZ214001';
STATUS
-------
VALID

BYS@ bys3>alter table order_info add(name varchar2(10));
Table altered.
BYS@ bys3>select status from dba_objects where object_name='KZCZ214001';
STATUS
-------
INVALID
索引失效后,1号锁还能查到。。。
BYS@ bys3>select SESSION_ID sid,OWNER,NAME,Type,MODE_HELD held,MODE_REQUESTED request from dba_ddl_locks WHERE NAME='KZCZ214001';
SID OWNER NAME TYPE HELD REQUEST
---------- ---------- ---------- ---------- --------- ---------
1 BYS KZCZ214001 Table/Proc Null None
edure/Type

####################################

等级共享锁 2 row share----rs

产生2号TM锁方法1:--手动锁定

把在19会话将test表设置为等级共享锁模式

BYS@ bys001>lock table test in row share mode;
Table(s) Locked.
可以查询到是在test表加了个模式2的锁
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 2 0 0
BYS@ bys001>select object_name from dba_objects where object_id=77389;
OBJECT_NAME
-------------------------------
TEST
在另一个会话147上做DML操作:
BYS@ bys001>select distinct sid from v$mystat;
SID
----------
147
BYS@ bys001>insert into test values(2);
1 row created.
BYS@ bys001>delete from test where a=1;
1 row deleted.
BYS@ bys001>select * from test;
A
----------
2
BYS@ bys001>update test set a=22 where a=2;
1 row updated.
BYS@ bys001>select * from test;
A
----------
22
在会话19上查询:
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 2 0 0
147 TM 77389 0 3 0 0

147 TX 196621 28393 6 0 0

如果使用DML语句,会报错:ORA-00054: resource busy and acquire with NOWAIT specified or timeout expired

产生2号TM锁方法2:--大表在线建索引

在会话1:--在大表上在线创建索引,要用ONLINE,不用ONLINE不会有2号锁。
BYS@ bys3>create index idx_test1 on test1(id) online;
Index created.
会话2:--有4号锁和2号锁
BYS@ bys3>select * from v$lock where sid=1;

ADDR KADDR SID TY ID1 ID2 LMODE REQUEST CTIME BLOCK
-------- -------- ---------- -- ---------- ---------- ---------- ---------- ---------- ----------
2AD66694 2AD666C0 1 AE 100 0 4 0 2154 0
2AD6697C 2AD669A8 1 DL 22325 0 3 0 4 0
2AD66AF0 2AD66B1C 1 OD 22325 0 4 0 4 0
2AD66C64 2AD66C90 1 DL 22325 0 3 0 4 0
B6A0DB98 B6A0DBC8 1 TM 22325 0 2 0 4 0
B6A0DB98 B6A0DBC8 1 TM 22354 0 4 0 4 0
2926D618 2926D690 1 TS 4 16777362 6 0 2 0
28471AE4 28471B24 1 TX 327696 2557 6 0
BYS@ bys3>col object_name for a20
BYS@ bys3>select a.sid,a.type,a.lmode,a.request,b.object_name from v$lock a,dba_objects b where a.id1=b.object_id and sid=1;
SID TY LMODE REQUEST OBJECT_NAME
---------- -- ---------- ---------- --------------------
1 TM 2 0 TEST1
1 TM 4 0 SYS_JOURNAL_22360
1 AE 4 0 ORA$BASE
1 OD 4 0 TEST1
1 DL 3 0 TEST1
1 DL 3 0 TEST1

小结:行级共享锁,是限制最少的TM锁,可以提供最高程度的并发性。其他会话可以对锁定的表进行任何类型的DML操作,还可以与其他会话锁并存。
################################################################################

等级排他锁 row exclusive table lock---RX 3

BYS@ bys001>select distinct sid from v$mystat;
SID
----------
19
BYS@ bys001>lock table test in row exclusive mode;
Table(s) Locked.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 3 0 0
3级锁是一个灵活性比较大的锁,insert delete update,for update 都可以产生一个3级锁,也允许其他事务来修改锁定的表
BYS@ bys001>select * from test;
A
----------
22
BYS@ bys001>update test set a=99 where a=22;
1 row updated.
BYS@ bys001>select * from test;
A
----------
99
BYS@ bys001>select distinct sid from v$mystat;
SID
----------
147
BYS@ bys001>insert into test values(55);
1 row created.
BYS@ bys001>select * from test;
A
----------
22
55
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 3 0 0
19 TX 655390 28214 6 0 0
147 TM 77389 0 3 0 0

147 TX 589824 28423 6 0 0

block列全部是0,没有阻塞。

此时,如执行DDL语句,报错:ORA-00054:resource busy and acquire with NOWAIT specified or timeout expired

小结:行级排他锁,通常已经有事务在修改行或者select…for update 修改结果集。允许其他事务对锁定的表进行select insert update delete 或 lock table 同时锁定一张表。

#####################################################################################

共享锁 share table lock 4

BYS@ bys001>select distinct sid from v$mystat;
SID
----------
19
BYS@ bys001>select * from test;
A
----------
99
55
BYS@ bys001>lock table test in row share mode;
Table(s) Locked.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 3 0 0
19 TX 655390 28214 6 0 0
模式标识:4
4级锁禁止其他会话对锁定的表进行DML操作但可以select查询,还允许多个事物一起持有
在会话147上进行删除操作,

BYS@ bys001>select distinct sid from v$mystat;
SID
----------
147
BYS@ bys001>DELETE TEST ;


BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 3 0 0
19 TX 655390 28214 6 0 1
147 TM 77389 0 3 0 0
147 TX 655390 28214 0 6 0
BYS@ bys001>lock table test in share mode;
Table(s) Locked.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 4 0 0
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 4 0 1
147 TM 77389 0 0 3 0

共享锁,其它事务可以查询锁定的表但不能修改,只允许当前事务修改,但可以多个事务持有它。

另一个产生4号锁的,见: --2号锁在线建索引实验。

##########################################################

TM锁5号锁实验:

BYS@ bys001>lock table test in share row exclusive mode;

Table(s) Locked.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 5 0 0
BYS@ bys001>select * from test;
no rows selected
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 5 0 0
BYS@ bys001>insert into test values(88);
1 row created.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 5 0 0
19 TX 524320 28676 6 0 0
在147会话执行DML操作会hang住
BYS@ bys001>insert into test values(88);
此时查询
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 5 0 1
19 TX 524320 28676 6 0 0
147 TM 77389 0 0 3 0

小结:共享行级排他锁,同一时间只允许一个事务持有和修改锁定的表,其他事务可以查询但不能修改。

5号锁--在存储过程运行中会出现:A B两个会话同时执行同一个存储过程时

session A exec p
session B exec p
#############################################

TM锁6号锁实验:

BYS@ bys001>lock table test in exclusive mode;

Table(s) Locked.
BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 6 0 0
在会话147进行hang住
BYS@ bys001>lock table test in row share mode; ---在此HANG住

BYS@ bys001>select sid,type,id1,id2,lmode,request,block from v$lock where type in('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
19 TM 77389 0 6 0 1
147 TM 77389 0 0 2 0

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