前阵子在漏洞扫描后，有些暂时不再使用的数据库链接Database Link需要删除。出于万一后续需要再用的情况考虑，于是乎先备份这些Database Link。首先让我想到的是直接生成DDL就行。事实上这DDL并不包含链接用户的密码。此路不通，所以就只能考虑用expdp工具来进行备份了。其次由于有些数据库用户的密码未知，因此这些用户创建的数据库链接在sys账号下无法删除。下文则是这些个问题的描述与解决。
一、环境准备
12c中包含了2个pdb数据库，分别是cdb1pdb1,cdb1pdb2
其中在cdb1pdb1上有一个db link指向了cdb1pdb2
--演示环境
sql> select * from v$version;
BANNER CON_ID
-------------------------------------------------------------------------------- ----------
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production 0
PL/sql Release 12.2.0.1.0 - Production 0
--在cdb1pdb2上创建用户，用户配置从cdb1pdb1访问
sql> alter session set container=cdb1pdb2;
sql> create user robin identified by xxx;
sql> grant dba,connect,resource to robin;
$ sqlplus robin/xxx@cdb1pdb2
sql> create table blog(ename varchar2(20),addr varchar2(60));
sql> insert into blog values('leshami','http://blog.csdn.net/leshami');
sql> commit;
--连接到cdb1pdb1，此时我们使用了hr账号，密码已知。
--真实的环境类似用户密码我们是未知的，此处演示。
$ sqlplus hr/hr@cdb1pdb1
sql> show user;
USER is "HR"
--创建到cdb1pdb2的数据库链接
sql> create database link to_cdb1pdb2 connect to robin identified by xxx using 'CDB1PDB2';
sql> select * from blog@to_cdb1pdb2;
ENAME ADDR
-------------------- ------------------------------------------------------------
leshami http://blog.csdn.net/leshami
二、备份数据库链接(提取DDL，以及导出DB Link)
通过get_ddl方式导出DB Link
$ sqlplus / as sysdba
sql> select db_link,username from cdb_db_links where owner='HR';
DB_LINK USERNAME
------------------------------ ----------------------------------------
TO_CDB1PDB2.YDQ05.COM ROBIN
sql> alter session set container=cdb1pdb1;
sql> alter session set current_schema=hr;
--通过get_ddl函数提取DDL，如下，我们看到密码部分为一个绑定变量
--很显然，这个没有起到绝对备份的作用
sql> set long 5000
sql> select dbms_Metadata.get_ddl('DB_LINK','TO_CDB1PDB2.YDQ05.COM','HR') FROM DUAL;
DBMS_MetaDATA.GET_DDL('DB_LINK','HR')
--------------------------------------------------------------------------------
CREATE DATABASE LINK "TO_CDB1PDB2.YDQ05.COM"
CONNECT TO "ROBIN" IDENTIFIED BY VALUES ':1'
USING 'CDB1PDB2'
通过expdp方式导出DB Link
$ vi prfile.par
directory=DATA_PUMP_DIR
dumpfile=hrdblink.dmp
logfile=exp_dblink.log
schemas=hr
INCLUDE=DB_LINK:"LIKE 'TO_CDB1PDB2.YDQ05.COM'"
$ expdp parfile=prfile.par
Export: Release 12.2.0.1.0 - Production on Tue Mar 27 17:38:11 2018
Copyright (c) 1982,2017,Oracle and/or its affiliates. All rights reserved.
Username: sys@cdb1pdb1 as sysdba
Password:
Connected to: Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
Starting "SYS"."SYS_EXPORT_SCHEMA_01": sys/********@cdb1pdb1 AS SYSDBA parfile=prfile.par
Processing object type SCHEMA_EXPORT/DB_LINK
Master table "SYS"."SYS_EXPORT_SCHEMA_01" successfully loaded/unloaded
******************************************************************************
Dump file set for SYS.SYS_EXPORT_SCHEMA_01 is:
/app/oracle/ora12c/admin/cdb1/dpdump/50DDF77203BA2CCBE053F401A8C03639/hrdblink.dmp
Job "SYS"."SYS_EXPORT_SCHEMA_01" successfully completed at Tue Mar 27 17:38:29 2018 elapsed 0 00:00:07
三、删除数据库链接(DB Link)
--此处模拟我们不知道创建数据库链接的用户名和密码，所以用sys登陆
sql> show user;
USER is "SYS"
sql> show con_name;
CON_NAME
------------------------------
CDB1PDB1
sql> alter session set current_schema=hr;
--以下操作均无法删除DB Link，即使带上owner也不行
sql> drop database link to_cdb1pdb2;
drop database link to_cdb1pdb2
*
ERROR at line 1:
ORA-01031: insufficient privileges
sql> drop database link TO_CDB1PDB2.YDQ05.COM;
drop database link TO_CDB1PDB2.YDQ05.COM
*
ERROR at line 1:
ORA-01031: insufficient privileges
--下面通过一个专用的存储过程来搞定
--关于这个使用sys删除其他用户下的dblink，感谢steve.tang支持提供了个参考链接
sql> exec DROP_DBLINK('HR','TO_CDB1PDB2.YDQ05.COM');
PL/sql procedure successfully completed.
sql> select db_link,username from cdb_db_links where owner='HR';
no rows selected
四、恢复数据库链接(DB Link)
$ impdp directory=DATA_PUMP_DIR dumpfile=hrdblink.dmp full=y
Import: Release 12.2.0.1.0 - Production on Wed Mar 28 09:15:11 2018
Copyright (c) 1982,Oracle and/or its affiliates. All rights reserved.
Username: sys@cdb1pdb1 as sysdba
Password:
Connected to: Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production
Master table "SYS"."SYS_IMPORT_FULL_01" successfully loaded/unloaded
Starting "SYS"."SYS_IMPORT_FULL_01": sys/********@cdb1pdb1 AS SYSDBA directory=DATA_PUMP_DIR dumpfile=hrdblink.dmp full=y
Processing object type SCHEMA_EXPORT/DB_LINK
Job "SYS"."SYS_IMPORT_FULL_01" successfully completed at Wed Mar 28 09:15:27 2018 elapsed 0 00:00:03
sql> conn hr/hr@cdb1pdb1
sql> select * from blog@to_cdb1pdb2;
ENAME ADDR
-------------------- ------------------------------------------------------------
leshami http://blog.csdn.net/leshami
