浅谈ORACLE数据库闪回

oracle 闪回技术包括闪回删除和闪回数据库。闪回删除主要是关注用户误删除表、索引的数据库对象；闪回数据库是一种快速的数据库恢复方案，这种恢复是基于用户的逻辑错误，比如对表中的数据做了错误的修改、插入了大量的错误数据。 闪回删除： [oracle@localh

oracle闪回技术包括闪回删除和闪回数据库。闪回删除主要是关注用户误删除表、索引的数据库对象；闪回数据库是一种快速的数据库恢复方案，这种恢复是基于用户的逻辑错误，比如对表中的数据做了错误的修改、插入了大量的错误数据。

闪回删除：

[oracle@localhost ~]$ sqlplus test/test@orcl

SQL*Plus: Release 10.2.0.4.0 - Production on Mon Jun 9 16:50:00 2014

Copyright (c) 1982, 2007, Oracle. All Rights Reserved.


Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>show parameter recyclebin;

NAME TYPE VALUE
---------------- ----------- ------------

recyclebin string on

SQL> drop table student;

Table dropped.

SQL> show recyclebin;
ORIGINAL NAME RECYCLEBIN NAMEOBJECT TYPE DROP TIME
---------------- ------------------------------ ------------ -------------------
STUDENT BIN$+2ROU1DktpLgQKjAkwBc6A==$0 TABLE 2014-06-09:16:50:41

SQL> select object_name,original_name,operationfrom recyclebin;

OBJECT_NAME
--------------------------------------------------------------------------------
ORIGINAL_NAME
--------------------------------------------------------------------------------
OPERATION
---------------------------
BIN$+2ROU1DltpLgQKjAkwBc6A==$0
STUDENT
DROP

SQL> select * from tab;

TNAME
--------------------------------------------------------------------------------
TABTYPE CLUSTERID
--------------------- ----------
BIN$+2ROU1DltpLgQKjAkwBc6A==$0
TABLE

SQL> flashback table student to before drop;

Flashback complete.

SQL> select * from tab;

TNAME
--------------------------------------------------------------------------------
TABTYPE CLUSTERID
--------------------- ----------
STUDENT
TABLE

SQL> select * from student;

SNO SNAME
---------- ------------------------------
1 xxx
11 aa

也可以执行下面语句进行闪回：

flashback table"BIN$+2ROU1DktpLgQKjAkwBc6A==$0" to before drop rename to student;

闪回数据库：

[oracle@localhost ~]$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.4.0 - Production on Mon Jun 9 16:50:00 2014

Copyright (c) 1982, 2007, Oracle. All Rights Reserved.

Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

查看数据库是否开闪回
SQL> select flashback_on from v$database;

FLASHBACK_ON
------------------
NO

SQL> alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38759: Database must be mounted by only one instance and not open.

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

SQL> startup mount
ORACLE instance started.

Total System Global Area 184549376 bytes
FixedSize 1218412 bytes
VariableSize 83888276 bytes
Database Buffers 96468992 bytes
RedoBuffers 2973696 bytes
Database mounted.

数据库在mount状态下再次尝试开启数据库的闪回功能，又返回错误信息，说明数据库在非归档状态下不支持数据库级别的闪回。
SQL> alter database flashback on;
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;

Database altered.

SQL> alter database flashback on;

Database altered.

SQL> alter database open;

Database altered.

开启归档，默认的归档目录：USE_DB_RECOVERY_FILE_DEST。
SQL> archive log list
Database logmode Archive Mode
Automaticarchival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 59
Next log sequence to archive 61
Current logsequence 61

检验数据库闪回是否开启
SQL> select flashback_on from v$database;

FLASHBACK_ON
------------------
YES

查看闪回区信息，默认安装大小为2G，根据数据库的具体情况作修改。
SQL> show parameter recover_file_dest

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest string /u01/app/oracle/flash_recovery_area
db_recovery_file_dest_size big integer 20G

数据库可以恢复到多少分钟以前，默认1440分钟（一天）
SQL> show parameter flash

NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_flashback_retention_target integer 1440

查看数据库能恢复到最早的scn和最早的时间
SQL> select oldest_flashback_scn,oldest_flashback_time fromv$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TIME
-------------------- ---------------------
1021372 20101130 23:07:18

SQL> select * from student;

SNO SNAME
---------- ------------------------------
1 xxx
11 aa

SQL> select current_scn from v$database;

CURRENT_SCN
-----------
6312445

SQL> insert into student values(22,'nn');

1 row created.

SQL> commit;

Commit complete.

SQL> select current_scn from v$database;

CURRENT_SCN
-----------
6312458

通过v$flashback_database_log和v$flashback_database_stat视图查询相关闪回数据库信息

SQL> selectoldest_flashback_scn,oldest_flashback_time from v$flashback_database_log;

OLDEST_FLASHBACK_SCN OLDEST_FLASHBAC
-------------------- ---------------
6259583 09-JUN-14

SQL> select * from v$flashback_database_stat;

BEGIN_TIME END_TIME FLASHBACK_DATA DB_DATA REDO_DATA
--------------- --------------- -------------- ---------- ----------
ESTIMATED_FLASHBACK_SIZE
------------------------
10-JUN-14 10-JUN-14 5529600 7790592 2463744

关闭数据库并启动到mount状态，执行闪回，并以resetlogs打开数据库

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

Total System Global Area 1224736768 bytes
Fixed Size 2083560 bytes
Variable Size 335545624 bytes
Database Buffers 872415232 bytes
Redo Buffers 14692352 bytes
Database mounted.
SQL> flashback database to scn 6312445;

Flashback complete.

SQL> alter database open resetlogs;

Database altered.

备注：

1、使用sysdba身份登陆，通过dba_recyclebin可以查询回收站里所有的对象，也可以指定条件查询

2、无论是OS认证还是密码认证，以sysdba登陆默认用户是sys，sys用户的默认表空间是system，system与sysaux表空间无法做回收站的操作

3、执行表闪回后，与表相关联的对象也会被闪回，但是对象名已经发生变化，需要重命名或者重建对象

4、只要启动了闪回数据库特性，数据库的永久表空间都会受到闪回数据库保护，如果不希望某个表空间受闪回数据库保护，可以禁用对某个表空间的闪回特性

alter tablespace users flashback off;

5、在闪回数据库时，往往要用到具体的时间或者scn，我们可以定义容易记忆的复原点（scn的别名）来执行闪回，步骤如下

5.1、创建一个复原点

SQL> create restore point rp0;

Restore point created.

5.2、创建有保证的复原点

SQL> create restore point rp1 guarantee flashbackdatabase;

Restore point created.

5.3、查询复原点信息

SQL> selectname,scn,storage_size,guarantee_flashback_database from v$restore_point;

NAME SCN STORAGE_SIZE GUARANTEE
---------- ------------ --------------------- ---------------------
RP1 6316026 31883264 YES

RP0 6322551 0 NO