当用户密码即将过期时，在登录时Oracle会提示ORA-28002错误，但是并不会影响正常的登录。
本来认为这个信息并没有太大的影响，但是没想到这个tb错误会导致SET AUTOTRACE功能失效：
solaris*orcl-/home/oracle$ sqlplus test/test
SQL*Plus: Release 11.2.0.3.0 Production on Fri Jul 13 11:27:28 2012
Copyright (c) 1982, 2011, Oracle. All rights reserved.
ERROR:
ORA-28002: the password will expire within 1 days
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
SQL> set autot on
ERROR:
ORA-28002: the password will expire within 1 days
SP2-0619: Error while connecting
SP2-0611: Error enabling STATISTICS report
SQL> alter user test identified by test;
User altered.
SQL> set autot on
ERROR:
ORA-24315: illegal attribute type
SP2-0619: Error while connecting
SP2-0611: Error enabling STATISTICS report
SQL> exit
Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
solaris*orcl-/home/oracle$ sqlplus test/test
SQL*Plus: Release 11.2.0.3.0 Production on Fri Jul 13 11:27:52 2012
Copyright (c) 1982, 2011, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
SQL> set autot on
SQL> insert into t values (1, 'a');
1 row created.
Execution Plan
----------------------------------------------------------
---------------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------------
| 0 | INSERT STATEMENT | | 1 | 12 | 1 (0)| 00:00:01 |
| 1 | LOAD TABLE CONVENTIONAL | T | | | | |
---------------------------------------------------------------------------------
Statistics
----------------------------------------------------------
71 recursive calls
9 db block gets
75 consistent gets
10 physical reads
1284 redo size
829 bytes sent via SQL*Net to client
785 bytes received via SQL*Net from client
3 SQL*Net roundtrips to/from client
9 sorts (memory)
0 sorts (disk)
1 rows processed
很显然，由于ORA-28002错误导致了SET AUTOTRACE ON功能启用时碰到了错误。当修改了当前的用户密码，则ORA-28002不再出现后，SET AUTOTRACE ON的功能恢复正常。
根据上面的信息其实可以判断，在启用SET AUTOTRACE ON功能时，sqlplus会自动创建一个新的会话来记录当前会话的统计信息。
而启用的新的会话会使用当前会话登录时保存的密码来进行登录，因此可以通过下面的例子来验证这个推论：
solaris*orcl-/home/oracle$ sqlplus test/test
SQL*Plus: Release 11.2.0.3.0 Production on Sun Jul 15 01:28:38 2012
Copyright (c) 1982, 2011, Oracle. All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, Oracle Label Security and Real Application Testing options
SQL> set autot on
SQL> set autot off
SQL> alter user test identified by test1;
User altered.
SQL> set autot on
ERROR:
ORA-01017: invalid username/password; logon denied
SP2-0619: Error while connecting
SP2-0611: Error enabling STATISTICS report
果然，在用户登录后，如果当前的密码被修改，是会导致SET AUTOTRACE ON启用时报错不正确的用户名密码错误的。