从ORACLE表空间offline谈起，表空间备份恢复
将表空间置为offline，可能的原因包括维护、备份恢复等目的；
表空间处于offline状态，那么Oracle不会允许任何对该表空间中对象的SQL执行，表空间置为offline时仍处于活动状态的语句在交易级别并不会受影响。
实验一：RMAN备份恢复表空间
SQL> create tablespace test datafile '/data/app/oracle/oradata/ORCL/datafile/test01.dbf' size 1G ;
Tablespace created.
SQL> alter tablespace TEST add datafile '/data/app/oracle/oradata/ORCL/datafile/test02.dbf' size 1G;
Tablespace altered.
[oracle@prod ~]$ rman target /
Recovery Manager: Release 12.1.0.2.0 - Production on Thu Jun 14 11:26:31 2018
Copyright (c) 1982, 2014, Oracle and/or its affiliates. All rights reserved.
connected to target database: ORCL (DBID=1607304684)
RMAN> backup tablespace "TEST" tag "test";
RMAN> alter tablespace test offline;
模拟数据文件损坏
[oracle@prod ~]$ mv /data/app/oracle/oradata/ORCL/datafile/test01.dbf /data/app/oracle/oradata/ORCL/datafile/test01.dbf.bk
[oracle@prod ~]$ mv /data/app/oracle/oradata/ORCL/datafile/test02.dbf /data/app/oracle/oradata/ORCL/datafile/test02.dbf.bk
利用RMAN进行介质恢复
[oracle@prod ~]$ rman target /
Recovery Manager: Release 12.1.0.2.0 - Production on Thu Jun 14 11:28:30 2018
Copyright (c) 1982, 2014, Oracle and/or its affiliates. All rights reserved.
connected to target database: ORCL (DBID=1607304684)
RMAN> restore tablespace "TEST";
RMAN> recover tablespace "TEST";
Starting recover at 14-JUN-18
using channel ORA_DISK_1
starting media recovery
media recovery complete, elapsed time: 00:00:00
Finished recover at 14-JUN-18
RMAN> alter tablespace test online;
Statement processed
RMAN>
实验二：expdp/impdp备份恢复表空间
SQL> create tablespace test datafile '/data/app/oracle/oradata/ORCL/datafile/test01.dbf' size 1G ;
Tablespace created.
SQL> alter tablespace TEST add datafile '/data/app/oracle/oradata/ORCL/datafile/test02.dbf' size 1G;
Tablespace altered.
RMAN> backup tablespace "TEST" tag "test";
RMAN> alter tablespace test offline;
SQL>drop tablespace test;
RMAN> restore tablespace test;
Starting restore at 14-JUN-18
using channel ORA_DISK_1
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of restore command at 06/14/2018 11:58:48
RMAN-20202: Tablespace not found in the recovery catalog
RMAN-06019: could not translate tablespace name "TEST"
因为rman是用来在介质故障之后进行恢复的，手动进行的drop表空间不是介质故障，而且执行drop操作的时候表空间信息已经被从数据字典里删掉
所以，只能找个地方，把整个库恢复到drop表空间之前，再用导出，导入的方法把这个表空间导入原来的库中
SQL> create user elon identified by "elon" default tablespace test account unlock;
User created.
SQL> grant dba to elon;
SQL> create table test as select * from user_objects where rownum < 10;
SQL> insert into test select * from test;
SQL> commit;
逻辑备份表空间TEST
[oracle@prod ~]$ expdp system/xxxxxx DIRECTORY=DUMP DUMPFILE=test.dmp TABLESPACES="test"
SQL> drop tablespace test including contents and datafiles;
进行恢复：
SQL> create tablespace test datafile '/data/app/oracle/oradata/HBCG/datafile/test01.dbf' size 1G ;
[oracle@prod ~]$ impdp system/oracle DIRECTORY=DUMP DUMPFILE=test.dmp
SQL> select tablespace_name,status from dba_tablespaces where tablespace_name='TEST';
TABLESPACE_NAME STATUS
------------------------------ ---------
TEST ONLINE