Oracle锁实验
MASICONG@orcl> select sid from v$mystat where rownum=1;
SID
----------
35
MASICONG@orcl> select sid from v$mystat where rownum=1;
SID
----------
1
1.分别模拟insert，update和delete造成阻塞的示例，并对v$lock中的相应的信息进行说明，给出SQL演示。
MASICONG@orcl> create table test (id varchar(2) primary key);
Table created.
INsert阻塞
MASICONG@orcl> insert into test values (10);
1 row created.
MASICONG@orcl> insert into test values(10); 另一个用户提交同样的请求就会卡住
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') ;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
1 TX 131090 674 0 4 0
35 TM 74571 0 3 0 0
1 TM 74571 0 3 0 0
1 TX 65540 508 6 0 0
35 TX 131090 674 6 0 1
说明1会话需要一个4级锁，但是35已经加了一个6级的锁阻塞了会话。因为会话1已经插入了一条记录，所以又一个TX锁可以通过。
MASICONG@orcl> select object_name from dba_objects where object_id=74571;
OBJECT_NAME
--------------------------------------------------------------------------------
TEST
通过TM知道目前是在一个表上加的锁，所有通过ID可以查到具体操作的是哪个表。
MASICONG@orcl> commit;
Commit complete.
MASICONG@orcl> insert into test values(10); 当一个会话提交后，另一个会话才能访问
*
ERROR at line 1:
ORA-00001: unique constraint (MASICONG.SYS_C0011055) violated
Update阻塞
MASICONG@orcl> commit
2 ;
Commit complete.
MASICONG@orcl> select * from test;
ID
--
1
10
MASICONG@orcl> update test set id=2 where id =1;
1 row updated.
MASICONG@orcl> update test set id=2 where id =1; 另一回话处于Block状态
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') ;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
1 TX 458775 552 0 6 0
1 TM 74571 0 3 0 0
35 TM 74571 0 3 0 0
35 TX 458775 552 6 0 1
显示出现了阻塞信息，会话在等待一个6级的锁
MASICONG@orcl> select sid,event from v$session_wait where sid in (1,35);
SID EVENT
---------- ----------------------------------------------------------------
1 enq: TX - row lock contention
35 SQL*Net message from client
上面标示1会话需要TX锁
DELETE操作
MASICONG@orcl> delete from test where id=10;
1 row deleted.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') ;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
1 TX 524289 908 0 6 0
35 TM 74571 0 3 0 0
1 TM 74571 0 3 0 0
35 TX 524289 908 6 0 1
说明1会话需要一个6级别的锁，但是被35会话的6级别的锁所阻塞。
2.模拟RI锁定导致阻塞的场景，并分析v$lock相应的锁定信息，给出SQL演示。
MASICONG@orcl> create table zhu (id number primary key);
Table created.
MASICONG@orcl> create table cong (id references zhu(id));
Table created.
MASICONG@orcl> insert into zhu values (1);
1 row created.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
35 TM 74573 0 3 0 0
35 TM 74575 0 3 0 0
35 TX 131087 676 6 0 0
这时候已经在主表和从表上都加了一个3级锁防止DDL操作，同时加了一个6级锁，防止DML操作。
MASICONG@orcl> insert into zhu values (1); 另一个会话也执行就会造成阻塞。
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
1 TM 74573 0 3 0 0
1 TM 74575 0 3 0 0
1 TX 262165 551 0 4 0
1 TX 589835 690 6 0 0
35 TM 74575 0 3 0 0
35 TM 74573 0 3 0 0
35 TX 262165 551 6 0 1
上面的实例说明有一行TX加了6级的锁没有阻塞，已经成功执行。主从表都加了3级的表锁。有一个因为要加一个4级锁而别6级锁阻塞，造成了等待。
MASICONG@orcl> update zhu set id =2 where id=1;
1 row updated.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
35 TM 74573 0 3 0 0
35 TX 327699 721 6 0 0
当更新主表的记录时候，只对主表上加了TM锁和TX锁。
MASICONG@orcl> delete from zhu where id =2;
1 row deleted.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
35 TM 74573 0 3 0 0
35 TX 393248 700 6 0 0
当删除主表内容时，只对主表加上了TM锁和TX锁
MASICONG@orcl> insert into zhu values (10);
1 row created.
MASICONG@orcl> insert into cong values (10);
1 row created.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
35 TM 74573 0 3 0 0
35 TM 74575 0 3 0 0
35 TX 393244 700 6 0 0
当从表插入的时候主表和从表都有3级的表锁还有一个6级的TX锁。
ASICONG@orcl> delete from cong where id=10
1 row deleted.
MASICONG@orcl> select sid,type,id1,id2,lmode,request,block from v$lock where type in ('TM','TX') order by 1,2;
SID TY ID1 ID2 LMODE REQUEST BLOCK
---------- -- ---------- ---------- ---------- ---------- ----------
35 TM 74573 0 3 0 0
35 TM 74575 0 3 0 0
35 TX 262165 551 6 0 0
当从表删除时，主表也有一个3级的锁在上面。
5.给出一个导致死锁的SQL示例。
场景：当同一张表，有两个会话，一个23，一个35，当23会话对表进行插入操作，插入数据1，35会话对表进行操作，插入数据2。之后23由对数据插入2,35会话插入数据1，就会造成阻塞，最后产生死锁。
MASICONG@orcl> select sid from v$mystat where rownum =1 ;
SID
----------
23
MASICONG@orcl> insert into test values (1);
1 row created.
MASICONG@orcl> insert into test values (2);
insert into test values (2)
*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource
MASICONG@orcl> select sid from v$mystat where rownum =1 ;
SID
----------
37
MASICONG@orcl> insert into test values (2);
1 row created.
MASICONG@orcl> insert into test values (1);
insert into test values (1)
*
ERROR at line 1:
ORA-01013: user requested cancel of current operation
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