Dblink 创建后字典表 dba_db_link 中只保存创建连接时使用用户名，密码不保存，实际上在 sys 用户下的另一张字典表 link$ 中保存了明文的用户密码，如果出现密码丢失或者不确认的情况，可以从中获取明文密码。

SQL> select * from link$ where name='CUSTOPR_BILL';

    OWNER# NAME                                                                                                                             CTIME
---------- -------------------------------------------------------------------------------------------------------------------------------- ---------
HOST
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
USERID                         PASSWORD                             FLAG AUTHUSR                        AUTHPWD
------------------------------ ------------------------------ ---------- ------------------------------ ------------------------------
        25 TO_BILL                                                                                                                     21-DEC-06
BILL
ACCSNAP                        123456                                0

SQL> quit