Oracle 闪回日志详解-优快云博客

本文链接：https://blog.youkuaiyun.com/jing_flower/article/details/76066629

本文深入探讨了Oracle数据库的闪回日志功能，它依赖于undo表空间，允许数据库进行时间点恢复，保障数据的安全性和一致性。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

闪回，读的是undo表空间

======================闪回日志===================================
SQL> show parameter undo

NAME                                 TYPE                   VALUE
------------------------------------ ---------------------- ------------------------------
undo_management                      string                 AUTO
undo_retention                       integer                900
undo_tablespace                      string                 UNDOTBS1
SQL>       
SQL> select log_mode from v$database;

LOG_MODE
------------------------
NOARCHIVELOG


SQL> archive log list
Database log mode              No Archive Mode                        //数据日志模式
Automatic archival             Disabled
Archive destination            USE_DB_RECOVERY_FILE_DEST              //归档终点
Oldest online log sequence     47
Current log sequence           49
SQL>    alter database flashback on
  2  ;
   alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38707: Media recovery is not enabled.


SQL> alter database archivelog;
alter database archivelog
*
ERROR at line 1:
ORA-01126: database must be mounted in this instance and not open in any instance


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

Total System Global Area 2388570112 bytes
Fixed Size                  2255472 bytes
Variable Size            1023411600 bytes
Database Buffers         1342177280 bytes
Redo Buffers               20725760 bytes
Database mounted.
SQL> alter database archivelog;

Database altered.

SQL> select open_mode from v$database;

OPEN_MODE
----------------------------------------
MOUNTED

SQL> alter database flashback on;       

Database altered.

SQL> select dbms_flashback.get_system_change_number from dual;

GET_SYSTEM_CHANGE_NUMBER
------------------------
                  815135

SQL> select to_char(systimestamp,'yyyy-mm-dd HH24:MI:SS') as sysdt from dual;

SYSDT
--------------------------------------
2017-07-25 12:35:42

SQL> truncate table test;

Table truncated.

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

Total System Global Area 2388570112 bytes
Fixed Size                  2255472 bytes
Variable Size            1023411600 bytes
Database Buffers         1342177280 bytes
Redo Buffers               20725760 bytes
Database mounted.
SQL> flashback database to scn 815135    //闪回数据库
  2  ;

Flashback complete.

SQL> alter database open read only;

Database altered.

SQL> select * from test;

ID
--------------------
4
7
100
900
5
1000
1100

7 rows selected.