先假設一種情況，假設有一個數據庫，數據量是2T。 如果要對這個數據庫進行遷移，在不考慮磁盤空間的前提下，要求在最短的時間內完成切換操作。
在不考慮磁盤空間前提下，備份時間，網絡傳輸時間，恢復時間。 這個時間對於7*24*365的系統來說，肯定是沒辦法承受的。
如果在考慮下備份空間+遷移後的空間。 這個對磁盤的開銷也是非常大。
在我的前一篇Blog裏，提到了RMAN的異機恢復，這種方法可以縮短我們DB的遷移時間。 但是空間問題還沒有解決。在這一篇，我們主要從遷移時間的角度來考慮這個問題。
RMAN 備份異機恢復 並創建新DBID
http://blog.csdn.net/tianlesoftware/archive/2011/03/11/6240983.aspx
在異機恢復中，我們最後對db 是用open resetlogs的方式打開的。
我們先看open resetlogs的影響:
（1）如果current online redo可以訪問，那麼對其進行歸檔操作。 然後清空所有online redo 的內容，並將日誌的序列設置爲1.
（2）如果online redo 不存在，就創建online redo。 這個位置是在控制文件裏記錄的。 我們在做RMAN 異機恢復的時候，驗證過這點。
（3）開始一個新的incarnation，初始化redo thread和 online redo 在控制文件中的記錄。
比如：將redo thread 的狀態設置爲closed，在redo thread的記錄中設置當前的log sequence 爲1. 設置每個redo thread 的checkpoint 到log sequence 1。
從每個thread 選擇一個redo log，並設置其sequence 爲1.
（4）在控制文件中更新當前所有的datafile 和online redo logs，及以後的歸檔文件用新的resetlog SCN 和 time stamp。
注意： open resetlogs 不會充值SCN.
一般用open resetlogs 打開數據庫之後，建議立即對數據庫進行一次備份。
下面是一個遷移的測試：
1. 在Target 庫rman 備份數據庫，並將備份copy到Auxiliary庫的相同位置
RMAN 的恢復對備份位置有講究，對於nocatalog模式下，這些備份的位置是寫在控制文件裏的。所以目錄結構要相同。
關於RMAN 的shell 備份腳本，參考：
Nocatalog 下的RMAN 增量備份 shell腳本
http://blog.csdn.net/tianlesoftware/archive/2011/01/26/6164931.aspx
[oracle@qs-dmm-rh1 backup]$ scp * 192.168.2.43:/u01/backup
[email protected]'s password:
arch_23m709vi_1_1_20110312 100% 6431KB 6.3MB/s 00:00
ctl_file_24m709vn_1_1_20110312 100% 9568KB 9.3MB/s 00:01
dave_lev0_1rm709u9_1_1_20110312 100% 610MB 12.0MB/s 00:51
dave_lev0_1sm709u9_1_1_20110312 100% 399MB 11.7MB/s 00:34
dave_lev0_1tm709u9_1_1_20110312 100% 4728KB 4.6MB/s 00:00
dave_lev0_1vm709uk_1_1_20110312 100% 1344KB 1.3MB/s 00:01
dave_spfile_25m709vp_1_1_20110312 100% 96KB 96.0KB/s 00:00
2. 在Auxiliary庫創建相關的目錄，口令文件，和初始化文件。
初始化文件可以直接從Target copy過來。如果目錄結構相同的話，都不用修改參數。
3. 用初始化文件將數據庫啓動到noumout狀態。
SQL> startup nomount pfile=?/dbs/initdave.ora
ORACLE instance started.
Total System Global Area 196681728 bytes
Fixed Size 1335444 bytes
Variable Size 83890028 bytes
Database Buffers 109051904 bytes
Redo Buffers 2404352 bytes
4. 恢復控制文件
RMAN> restore controlfile from '/u01/backup/ctl_file_2qm72jcf_1_1_20110312';
Starting restore at 12-MAR-11
using channel ORA_DISK_1
channel ORA_DISK_1: restoring control file
channel ORA_DISK_1: restore complete, elapsed time: 00:00:02
output file name=/u01/oradata/control01.ctl
output file name=/u01/oradata/control02.ctl
output file name=/u01/oradata/control03.ctl
Finished restore at 12-MAR-11
5. 將數據庫啓動到mout狀態
SQL> alter database mount;
Database altered.
6. restore 數據庫
RMAN> restore database;
Starting restore at 12-MAR-11
released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=20 device type=DISK
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00003 to /u01/app/oracle/oradata/dave/undotbs01.dbf
channel ORA_DISK_1: reading from backup piece /u01/backup/dave_lev0_28m70ar0_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/dave_lev0_28m70ar0_1_1_20110312 tag=DAVE_LEV0
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00004 to /u01/app/oracle/oradata/dave/users01.dbf
channel ORA_DISK_1: reading from backup piece /u01/backup/dave_lev0_2am70ara_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/dave_lev0_2am70ara_1_1_20110312 tag=DAVE_LEV0
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00002 to /u01/app/oracle/oradata/dave/sysaux01.dbf
channel ORA_DISK_1: reading from backup piece /u01/backup/dave_lev0_27m70ar0_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/dave_lev0_27m70ar0_1_1_20110312 tag=DAVE_LEV0
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:25
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00001 to /u01/app/oracle/oradata/dave/system01.dbf
channel ORA_DISK_1: reading from backup piece /u01/backup/dave_lev0_26m70ar0_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/dave_lev0_26m70ar0_1_1_20110312 tag=DAVE_LEV0
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:25
Finished restore at 12-MAR-11
7. recover 數據庫
RMAN> recover database;
Starting recover at 12-MAR-11
using channel ORA_DISK_1
starting media recovery
channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=24
channel ORA_DISK_1: reading from backup piece /u01/backup/arch_2cm70as8_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/arch_2cm70as8_1_1_20110312 tag=ARC_BAK
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
archived log file name=/u01/app/oracle/product/11.2.0/dbhome_1/dbs/arch1_24_745352047.dbf thread=1 sequence=24
channel ORA_DISK_1: starting archived log restore to default destination
channel ORA_DISK_1: restoring archived log
archived log thread=1 sequence=25
channel ORA_DISK_1: reading from backup piece /u01/backup/arch_2dm70as8_1_1_20110312
channel ORA_DISK_1: piece handle=/u01/backup/arch_2dm70as8_1_1_20110312 tag=ARC_BAK
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
archived log file name=/u01/app/oracle/product/11.2.0/dbhome_1/dbs/arch1_25_745352047.dbf thread=1 sequence=25
unable to find archived log
archived log thread=1 sequence=26
RMAN-00571: ===========================================================
RMAN-00569: =============== ERROR MESSAGE STACK FOLLOWS ===============
RMAN-00571: ===========================================================
RMAN-03002: failure of recover command at 03/12/2011 00:58:04
RMAN-06054: media recovery requesting unknown archived log for thread 1 with sequence 26 and starting SCN of 1055401
8. 在主庫進行一些事務操作
SQL> create table anhui as select * from all_tables;
Table created.
SQL> commit;
Commit complete.
SQL> alter system switch logfile;
System altered.
9. 關閉主庫，迅速把主庫的歸檔文件和online redo 複製到Auxiliary庫
[oracle@qs-dmm-rh1 archivelog]$ scp * 192.168.2.43:/u01/archivelog
[email protected]'s password:
1_26_745352047.dbf 100% 1509KB 1.5MB/s 00:00
[oracle@qs-dmm-rh1 dave]$ scp redo* 192.168.2.43:/u01/app/oracle/oradata/dave/
[email protected]'s password:
redo01.log 100% 50MB 16.7MB/s 00:03
redo02.log 100% 50MB 12.5MB/s 00:04
redo03.log 100% 50MB 12.5MB/s 00:04
[oracle@qs-dmm-rh1 dave]$
10. 再次recover database
RMAN> recover database;
Starting recover at 12-MAR-11
using channel ORA_DISK_1
starting media recovery
archived log for thread 1 with sequence 26 is already on disk as file /u01/app/oracle/oradata/dave/redo02.log
archived log for thread 1 with sequence 27 is already on disk as file /u01/app/oracle/oradata/dave/redo03.log
archived log file name=/u01/app/oracle/oradata/dave/redo02.log thread=1 sequence=26
archived log file name=/u01/app/oracle/oradata/dave/redo03.log thread=1 sequence=27
media recovery complete, elapsed time: 00:00:05
Finished recover at 12-MAR-11
11. 打開數據庫
SQL>alter database open resetlogs;
SQL> select count(*) from dave;
COUNT(*)
----------
71157
12. 重建Temp 表空間
在恢復的時候，會自動創建TEMP 表空間。但是和布豆聊到這個問題的時候，他說這個temp 文件好像沒有起到作用。 尤其是數據量大的時候，所以他建議重建添加temp 數據文件。
SQL> select name from v$tempfile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/dave/temp01.dbf
SQL> alter tablespace temp add tempfile '/u01/app/oracle/oradata/dave/temp02.dbf ' size 8192M;
Tablespace altered.
SQL> select name from v$tempfile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/dave/temp01.dbf
/u01/app/oracle/oradata/dave/temp02.dbf
SQL> alter database tempfile '/u01/app/oracle/oradata/dave/temp01.dbf' offline;
Database altered.
SQL> alter database tempfile '/u01/app/oracle/oradata/dave/temp01.dbf' drop including datafiles;
Database altered.
SQL> select name from v$tempfile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/dave/temp02.dbf