【转】外键缺少索引引发的死锁

客户的10.2.0.4 RAC for AIX环境频繁出现ORA-60死锁问题，导致应用程序无法顺利执行。


经过一系列的诊断，发现最终问题是由于外键上没有建立索引所致，由于程序在主子表上删除数据，缺少索引导致行级锁升级为表级锁，最终导致大量的锁等待和死锁。

下面通过一个例子简单模拟一下问题：

SQL> create table t_p (id number primary key, name varchar2(30));

Table created.

SQL> create table t_f (fid number, f_name varchar2(30), foreign key (fid) references t_p);

Table created.

SQL> insert into t_p values (1, 'a');

1 row created.

SQL> insert into t_f values (1, 'a');

1 row created.

SQL> insert into t_p values (2, 'b');

1 row created.

SQL> insert into t_f values (2, 'c');

1 row created.

SQL> commit;

Commit complete.

SQL> delete t_f where fid = 2;

1 row deleted.

这时在会话2同样对子表进行删除：

SQL2> delete t_f where fid = 1;

1 row deleted.

回到会话1执行主表的删除：

SQL> delete t_p where id = 2;

会话被锁，回到会话2执行主表的删除：

SQL2> delete t_p where id = 1;

会话同样被锁，这时会话1的语句被回滚，出现ORA-60死锁错误：

delete t_p where id = 2
*
ERROR at line 1:
ORA-00060: deadlock detected while waiting for resource


SQL> rollback;

Rollback complete.

将会话1操作回滚，会话2同样回滚并建立外键列上的索引：


1 row deleted.

SQL2> rollback;

Rollback complete.

SQL2> create index ind_t_f_fid on t_f(fid);

Index created.

重复上面的步骤会话1删除子表记录：

SQL> delete t_f where fid = 2;

1 row deleted.

会话2删除子表记录：

SQL2> delete t_f where fid = 1;

1 row deleted.

会话1删除主表记录：

SQL> delete t_p where id = 2;

1 row deleted.

会话2删除主表记录：

SQL> delete t_p where id = 1;

1 row deleted.

所有的删除操作都可以成功执行，关于两种情况下锁信息的不同这里就不深入分析了，重点就是在外键列上建立索引。

虽然有一些文章提到过，如果满足某些情况，可以不在外键列上建立的索引，但是我的观点一向是，既然创建了外键，就不要在乎再多一个索引，因为一个索引所增加的代价，与缺失这个索引所带来的问题相比，是微不足道的。

参考：
http://yangtingkun.itpub.net/post/468/524858
http://www.cnblogs.com/angzi/archive/2006/12/09/587612.html


【补充】Oracle 10g和Oracle 9i trc日志内容的差别

Oracle 10g 10.2.0.3.0：

DEADLOCK DETECTED ( ORA-00060 )
[Transaction Deadlock]
The following deadlock is not an ORACLE error. It is a
deadlock due to user error in the design of an application
or from issuing incorrect ad-hoc SQL. The following
information may aid in determining the deadlock:
Deadlock graph:
                       ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
TM-0000dd55-00000000        16     146    SX   SSX       17     148    SX   SSX
TM-0000dd55-00000000        17     148    SX   SSX       16     146    SX   SSX
session 146: DID 0001-0010-00000008	session 148: DID 0001-0011-00000006
session 148: DID 0001-0011-00000006	session 146: DID 0001-0010-00000008
Rows waited on:
Session 148: no row
Session 146: no row
Information on the OTHER waiting sessions:
Session 148:
  pid=17 serial=39 audsid=540046 user: 54/SCOTT
  O/S info: user: SKYHOME\sky, term: SKYHOME, ospid: 3028:7000, machine: WORKGROUP\SKYHOME
            program: plsqldev.exe
  application name: PL/SQL Developer, hash value=1190136663
  action name: Command Window - New, hash value=254318129
  Current SQL Statement:
  
delete t_p where id = 1
End of information on OTHER waiting sessions.
Current SQL statement for this session:
delete t_p where id = 2

Oracle 9i 9.2.0.7.0：

DEADLOCK DETECTED
Current SQL statement for this session:
delete t_p where id = 2
The following deadlock is not an ORACLE error. It is a
deadlock due to user error in the design of an application
or from issuing incorrect ad-hoc SQL. The following
information may aid in determining the deadlock:
Deadlock graph:
                       ---------Blocker(s)--------  ---------Waiter(s)---------
Resource Name          process session holds waits  process session holds waits
TM-0000260e-00000000        21      51    SX   SSX       23      20    SX   SSX
TM-0000260e-00000000        23      20    SX   SSX       21      51    SX   SSX
session 51: DID 0001-0015-0000043D	session 20: DID 0001-0017-00000397
session 20: DID 0001-0017-00000397	session 51: DID 0001-0015-0000043D
Rows waited on:
Session 20: no row
Session 51: no row
Information on the OTHER waiting sessions:
Session 20:
  pid=23 serial=53179 audsid=197296 user: 87/scott
  O/S info: user: sky, term: SKYHOME, ospid: 5540:4984, machine: WORKGROUP\SKYHOME
            program: plsqldev.exe
  client info: 127.0.0.1
  application name: PL/SQL Developer, hash value=1190136663
  action name: Command Window - New, hash value=254318129
  Current SQL Statement:
  
delete t_p where id = 1
End of information on OTHER waiting sessions.