DB link的迁移（dblink中的密码未知）
不知DBA有时候是否会遇到这样的尬尴局面，做某些Schema的迁移的时候，由于用到Public的db link，然而由于不知道db link中目标端账号的密码，因此无法在新环境重新创建DB link。
本次实验的思路是将视图dba_db_links的基表link$迁移到出来并替换到新环境。因为用户的password密文保存在link$基表中。
----首先交代两边环境，都是Linux上11.2.0.3的版本，在10.2.0.4上也测试过。
一边数据库seven，一边数据库ginna。假设在不知道scott的密码情况下将seven端的名为test的db link迁移至ginna端。
源端操作：
首先还在源端创建一个public 的db link 名为test。
seven >create public database link test connect to scott identified by tiger using 'ginna'; Database link created. seven >select * from global_name@test; GLOBAL_NAME --------------------- GINNA seven >select * from dba_db_links; OWNER DB_LINK USERNAME HOST CREATED ------------------------------ ------------------------------ ------------------------------ ------------------------------ --------- PUBLIC TEST SCOTT ginna 06-MAR-15
创建中间表trans1，CTAS基表sys.link$。
seven >create table trans1 as select * from sys.link$;
Table created.
seven >select count(*) from trans1;
COUNT(*)
----------
1
然后在seven用户下创建第二个中间表trans2,（seven 有dba权限）。
seven >conn seven/oracle
Connected.
seven >create table trans2 as select * from sys.link$; -----当然不能直接CTAS基表的。
create table trans2 as select * from sys.link$
*
ERROR at line 1:
ORA-01031: insufficient privileges
seven >create table trans2 as select * from sys.trans1;
Table created.
seven >select count(*) from trans2;
COUNT(*)
----------
1
seven >
OK，中间表trans2创建成功。
目标端操作：
在目标端创建名为test2的Public db link。
ginna >show user USER is "SYS" ginna >select * from dba_db_links; no rows selected ginna >create public database link test2 connect to seven identified by oracle using 'seven'; Database link created. ginna >select * from global_name@test2; GLOBAL_NAME ---------------------- SEVEN ginna >set line 200 ginna >col db_link for a30 ginna >col host for a30 ginna >select * from dba_db_links; OWNER DB_LINK USERNAME HOST CREATED ------------------------------ ------------------------------ ------------------------------ ------------------------------ --------- PUBLIC TEST2 SEVEN seven 06-MAR-15
ginna >create table trans3 as select * from trans2@test2;
Table created.
ginna >select count(*) from trans3;
COUNT(*)
----------
1
ginna >truncate table sys.link$; Table truncated. ginna >insert into sys.link$ select * from trans3; 1 row created. ginna >commit; Commit complete.
现在再查一下dba_db_links就可以发现名为test的db link已经成功迁移在ginna端。
ginna >select * from dba_db_links; OWNER DB_LINK USERNAME HOST CREATED ------------------------------ ------------------------------ ------------------------------ ------------------------------ --------- PUBLIC TEST SCOTT ginna 06-MAR-15
测试db link 的有效性：
ginna >select * from global_name@test; GLOBAL_NAME ------------------ GINNA
显然是不能的：
ginna >create public database link test2 connect to seven identified by oracle using 'seven';
create public database link test2 connect to seven identified by oracle using 'seven'
*
ERROR at line 1:
ORA-02011: duplicate database link name
前提需要刷新下shared pool。之后再重建就可以了。
ginna >alter system flush shared_pool; System altered. ginna >create public database link test2 connect to seven identified by oracle using 'seven'; Database link created. ginna >select * from dba_db_links; OWNER DB_LINK USERNAME HOST CREATED ------------------------------ ------------------------------ ------------------------------ ------------------------------ --------- PUBLIC TEST SCOTT ginna 06-MAR-15 PUBLIC TEST2 SEVEN seven 06-MAR-15 ginna >
当然如果不flush shared pool的话直接删除db link则会遭遇ora-600内部报错：
SQL> drop public database link test2;
drop public database link test2
*
ERROR at line 1:
ORA-00603: ORACLE server session terminated by fatal error
ORA-00600: internal error code, arguments: [16500], [kqdDBLinkUpdate], [3], [0], [TEST2], [], [], [], [], [], [], []
Process ID: 11165
Session ID: 152 Serial number: 359
SQL>
SQL> create public database link test2 connect to seven identified by oracle using 'seven';
ERROR:
ORA-03114: not connected to ORACLE
SQL> conn / as sysdba
Connected.
SQL> create public database link test2 connect to seven identified by oracle using 'seven';
Database link created.
SQL> drop public database link test2;
Database link dropped.
SQL>
当然我们也可以不创建test2这个db link，主要就是将trans1这张中间表迁移至ginna库就可以了，这有很多方法，可以直接使用exp/imp或者数据泵都可以。条条大道通罗马，方法有很多种，主要就是将seven端的sys.link$基表迁移至ginna端并替换掉ginna端的sys.link$。