Oracle锁实验

MASICONG@orclselectsidfromv$mystatwhererownum=1;SID----------35MASICONG@orclselectsidfromv$mystatwhererownum=1;SID---..

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，网站空间，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

---------- -- ---------- ---------- ---------- ---------- ----------