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