ORACLEFLASHBACKDATABASE总结(四)

当进行闪回时，先恢复到对应target time，即我们的之前的某个镜像上，然后根据redo log，重新应用redo log，将数据恢复到我们指定的闪回的时间点上。从这里可以看出，闪回数据库是需要redo log和归档日志支持的。

闪回数据库的限制

1：闪回数据库不能用于介质恢复

2：闪回数据库不能用于恢复使用了shrink技术的数据文件，不能用于恢复已经删除的数据文件

3：不能从重建控制文件或者恢复的控制文件，进行闪回数据库，因为控制文件中的闪回日志信息被过期丢弃了

4：我们不能使用闪回数据库将数据库闪回到执行nologging操作的时间点，因为有可能会造成数据快损坏

模拟一下控制文件恢复的情景：

[oraele@vm1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.3.0 Production on Tue Jan 27 09:13:12 2015

Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> recover database using backup controlfile;
ORA-00279: change 1138457 generated at 01/26/2015 16:10:27 needed for thread 1
ORA-00289: suggestion :
/u01/app/oraele/fast_recovery_area/ORCL/archivelog/2015_01_27/o1_mf_1_1_%u_.arc
ORA-00280: change 1138457 for thread 1 is in sequence #1


Specify log: {=suggested | filename | AUTO | CANCEL}
/u01/app/oraele/oradata/orcl/redo01.log
Log applied.
Media recovery complete.
SQL> alter database open resetlogs;

Database altered.

SQL> select * from test;

        ID SCN
---------- --------------------
         0 1121575
         1 1126681
         2 1138419
         3 1150711

SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  267227136 bytes
Fixed Size                  2227504 bytes
Variable Size             192938704 bytes
Database Buffers           67108864 bytes
Redo Buffers                4952064 bytes
Database mounted.
SQL> flashback database to scn 1138419;
flashback database to scn 1138419
*
ERROR at line 1:
ORA-38729: Not enough flashback database log data to do FLASHBACK.

SQL> desc v$flashback_database_log
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 OLDEST_FLASHBACK_SCN                               NUMBER
 OLDEST_FLASHBACK_TIME                              DATE
 RETENTION_TARGET                                   NUMBER
 FLASHBACK_SIZE                                     NUMBER
 ESTIMATED_FLASHBACK_SIZE                           NUMBER

SQL> select olddest_flashback_scn from v$flashback_database_log;
select olddest_flashback_scn from v$flashback_database_log
       *
ERROR at line 1:
ORA-00904: "OLDDEST_FLASHBACK_SCN": invalid identifier


SQL> c/oldd/old
  1* select oldest_flashback_scn from v$flashback_database_log
SQL> /

OLDEST_FLASHBACK_SCN
--------------------
             1150901

SQL>

SQL> select begin_time from v$flashback_database_stat;

BEGIN_TIM
---------
27-JAN-15