DB link的遷移（dblink中的密碼未知）

    不知DBA有時候是否會遇到這樣的尬尷局面，作某些Schema的遷移的時候，因爲用到Public的db link，然而因爲不知道db link中目標端帳號的密碼，所以沒法在新環境從新建立DB link。

本次實驗的思路是將視圖dba_db_links的基表link$遷移到出來並替換到新環境。由於用戶的password密文保存在link$基表中。

----首先交代兩邊環境，都是Linux上11.2.0.3的版本，在10.2.0.4上也測試過。

一邊數據庫seven，一邊數據庫ginna。假設在不知道scott的密碼狀況下將seven端的名爲test的db link遷移至ginna端。

源端操做：

首先還在源端建立一個public 的db link 名爲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

建立中間表trans1，CTAS基表sys.link$。

seven >create table trans1 as select * from sys.link$;

Table created.

seven >select count(*) from trans1;

  COUNT(*)
----------
         1

而後在seven用戶下建立第二個中間表trans2,（seven 有dba權限）。

seven >conn seven/oracle
Connected.
seven >create table trans2 as select * from sys.link$;   -----固然不能直接CTAS基表的。
create table trans2 as select * from sys.link$
                                         *
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，中間表trans2建立成功。

目標端操做：

在目標端建立名爲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

經過test2的db link將seven端的trans2表CTAS到表trans3。

ginna >create table trans3 as select * from trans2@test2;

Table created.

ginna >select count(*) from trans3;

  COUNT(*)
----------
         1

truncate掉基表sys.link$,爲了安全起見也能夠先備份下基表，並將表trans3插入到基表link$中。

ginna >truncate table sys.link$;

Table truncated.

ginna >insert into sys.link$ select * from trans3;

1 row created.

ginna >commit;

Commit complete.

如今再查一下dba_db_links就能夠發現名爲test的db link已經成功遷移在ginna端。

ginna >select * from dba_db_links;

OWNER                          DB_LINK                        USERNAME                       HOST                           CREATED
------------------------------ ------------------------------ ------------------------------ ------------------------------ ---------
PUBLIC                         TEST                           SCOTT                          ginna                          06-MAR-15

測試db link 的有效性：

ginna >select * from global_name@test;

GLOBAL_NAME
------------------
GINNA

OK，如今還有一個問題，以前名爲test2的db link如今仍是否存在？是否能重建？

顯然是不能的：

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

前提須要刷新下shared pool。以後再重建就能夠了。

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 >

固然若是不flush shared pool的話直接刪除db link則會遭遇ora-600內部報錯：

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> 

固然咱們也能夠不建立test2這個db link，主要就是將trans1這張中間表遷移至ginna庫就能夠了，這有不少方法，能夠直接使用exp/imp或者數據泵均可以。條條大道通羅馬，方法有不少種，主要就是將seven端的sys.link$基表遷移至ginna端並替換掉ginna端的sys.link$。