有些朋友创建了一个非public的dblink，现在该数据库的其他用户需要去使用该dblink，在正常情况下无访问权限，需要重新建一个dblink，或者将原dblink修改为public。但是由于忘记了原dblink的目标段的密码，使得创建或者修改dblink的步骤无法进行下去。这里通过修改基表(link$)，解决该问题。
创建dblink
SQL> show user;
USER is "SYS"
SQL> create database link "xff_dblink"
2 connect to TEST
3 identified by "test"
4 using '11.1.1.1:1521/mcrm';
Database link created.
SQL> select * from dba_db_links where db_link like 'XFF_DBLINK%';
OWNER DB_LINK USERN HOST CREATED
----- ------------------------------------------- ----- ------------------ --------
SYS XFF_DBLINK.REGRESS.RDBMS.DEV.US.ORACLE.COM TEST 11.1.1.1:1521/mcrm 29-MAR-12
SQL> select sysdate from dual@xff_dblink;
SYSDATE
---------
29-MAR-12
SQL> CONN TEST/TEST
Connected.
SQL> SELECT SYSDATE FROM DUAL@XFF_DBLINK;
SELECT SYSDATE FROM DUAL@XFF_DBLINK
*
ERROR at line 1:
ORA-02019: connection description for remote database not found
--该dblink不是public的，所以test用户无权访问
dblink变为public类型
SQL> CONN / AS SYSDBA
Connected.
SQL> set long 1000
SQL> select text from dba_views where view_name='DBA_DB_LINKS';
TEXT
-------------------------------------------------------------------
select u.name, l.name, l.userid, l.host, l.ctime
from sys.link$ l, sys.user$ u
where l.owner# = u.user#
--查询出dblink相关的基表有link$和user$
SQL> desc sys.link$
Name Null? Type
----------------------------- -------- --------------------
OWNER# NOT NULL NUMBER
NAME NOT NULL VARCHAR2(128)
CTIME NOT NULL DATE
HOST VARCHAR2(2000)
USERID VARCHAR2(30)
PASSWORD VARCHAR2(30)
FLAG NUMBER
AUTHUSR VARCHAR2(30)
AUTHPWD VARCHAR2(30)
PASSWORDX RAW(128)
AUTHPWDX RAW(128)
SQL> select owner# from sys.link$ where name like 'XFF_DBLINK%';
OWNER#
----------
0
--XFF_DBLINK对应的用户标识记录在link$.owner#中
SQL> SELECT USER#,NAME FROM USER$ WHERE name in ('SYS','PUBLIC');
USER# NAME
---------- ------------------------------
1 PUBLIC
0 SYS
--现link$.owner#值为0，表示该dblink所属用户为SYS，现在让该dblink变为public
--现需要让该dblink变为public，需要做的是修改link$.owner#的值为1
SQL> UPDATE LINK$ SET OWNER#=1 WHERE name like 'XFF_DBLINK%';
1 row updated.
SQL> COMMIT;
Commit complete.
--需要刷新shared_pool
SQL> ALTER SYSTEM FLUSH SHARED_POOL;
System altered.
--查看dblink所属者，已经修改为public
SQL> select owner from dba_db_links where db_link like 'XFF_DBLINK%';
OWNER
----------
PUBLIC
--测试dblink是否成功
SQL> CONN TEST/TEST
Connected.
SQL> SELECT SYSDATE FROM DUAL@XFF_DBLINK;
SYSDATE
---------
29-MAR-12
