基于Oracle闪回详解(必看篇)

Oracle 9i 开始支持闪回，Oracle10g开始全面支持闪回功能，Oracle11g有所完善，为大家快速的恢复数据，查询历史数据提供了很大的便捷方法。

本文主要对Oracle常用闪回使用做些详细介绍，其中对于不常用的事务和版本闪回，这里就不做介绍

一、Oracle闪回概述

二、Oracle闪回使用详解

1、闪回开启

(1)开启闪回必要条件

a.开启归档日志

如未开启，在mount状态执行alter database archivelog;

b.设置合理的闪回区

db_recovery_file_dest：指定闪回恢复区的位置

db_recovery_file_dest_size：指定闪回恢复区的可用空间大小

db_flashback_retention_target：指定数据库可以回退的时间，单位为分钟，默认1440分钟(1天),实际取决于闪回区大小

(2)检查是否开启闪回

(3)开启闪回

a.开启归档

b.设置闪回区

c.开启flashback (10g在mount开启)

(4)确定闪回开启

(5)关闭闪回

2、闪回使用

(1)闪回查询

闪回查询主要是根据Undo表空间数据进行多版本查询，针对v$和x$动态性能视图无效，但对DBA_、ALL_、USER_是有效的

a.闪回查询

允许用户查询过去某个时间点的数据，用以重构由于意外删除或更改的数据，数据不会变化。

DEPTNO DNAME LOC

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO
OPERATIONS BOSTON
SQL> select * from scott.dept as of timestamp to_timestamp('2017-12-14 16:20:00','yyyy-mm-dd hh24:mi:ss');

DEPTNO DNAME LOC

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO
OPERATIONS BOSTON

SQL> select * from scott.dept as of scn 16801523;

DEPTNO DNAME LOC

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO
OPERATIONS BOSTON

b.闪回版本查询

用于查询行级数据库随时间变化的方法

c.闪回事务查询

用于提供查看事务级别数据库变化的方法

(2)闪回表(update/insert/delete)

闪回表就是对表的数据做回退，回退到之前的某个时间点，其利用的是undo的历史数据，与undo_retention设置有关，默认是14400分钟（1天）

同样，sys用户表空间不支持闪回表,要想表闪回，需要允许表启动行迁移(row movement)

闪回表示例：

SQL> select row_movement from dba_tables where table_name='DEPT' and owner='SCOTT';
ROW_MOVE

DISABLED
SQL> alter table scott.dept enable row movement;
Table altered.

SQL> flashback table scott.dept to timestamp to_timestamp('2017-12-14 16:20:00','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
SQL> select * from scott.dept;
DEPTNO DNAME LOC

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO
OPERATIONS BOSTON
SQL> alter table scott.dept disable row movement;
Table altered.

(3)闪回DROP(drop table)

当一个表被drop掉，表会被放入recyclebin回收站，可通过回收站做表的闪回。表上的索引、约束等同样会被恢复

不支持sys/system用户表空间对象，可通过alter system set recyclebin=off;关闭回收站功能

闪回DROP示例：

ID NAME

2
4

SQL> drop table t;

Table dropped.

SQL> show recyclebin;
ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME

T BIN$YEh2QcvZdJLgUxyAgQpnVQ==$0 TABLE 2017-12-14:15:02:06
SQL> flashback table t to before drop;

Flashback complete.

SQL> select * from t;

ID NAME

2
4

备注：即使不开始flashback，只要开启了recyclebin，那么就可以闪回DROP表。

但如果连续覆盖，就需要指定恢复的表名，如果已经存在表，则需要恢复重命名。

(4)闪回数据库(truncate/多表数据变更)

数据库闪回必须在mounted状态下进行，基于快照的可以再open下进行闪回库

闪回数据库主要是将数据库还原值过去的某个时间点或SCN，用于数据库出现逻辑错误时，需要open database resetlogs

a.全库闪回

数据库闪回示例

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

SMITH CLERK 7902 1980-12-17 00:00:00 800 20
ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
KING PRESIDENT 1981-11-17 00:00:00 5000 10
TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
JAMES CLERK 7698 1981-12-03 00:00:00 950 30
FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
rows selected.

SQL> truncate table scott.EMP;

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

Total System Global Area 9.4067E+10 bytes
Fixed Size 2263936 bytes
Variable Size 9395242112 bytes
Database Buffers 8.4557E+10 bytes
Redo Buffers 112766976 bytes
Database mounted.
SQL> flashback database to timestamp to_timestamp('2017-12-14 14:12:46','yyyy-mm-dd HH24:MI:SS');

Flashback complete.
SQL> alter database open resetlogs;

Database altered.

SQL> select * from scott.emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

SMITH CLERK 7902 1980-12-17 00:00:00 800 20
ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
KING PRESIDENT 1981-11-17 00:00:00 5000 10
TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
JAMES CLERK 7698 1981-12-03 00:00:00 950 30
FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
rows selected.

b.快照闪回

针对主库和备库都可以创建闪回快照点，然后恢复到指定的快照点，但主库一旦恢复到快照点，备库的同步则需要重新同步

DEPTNO DNAME LOC ADDR

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO

SQL> create restore point before_201712151111 guarantee flashback database;
Restore point created.

SQL> create table scott.t as select * from scott.dept;
Table created.

SQL> truncate table scott.t;
Table truncated.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area 9.4067E+10 bytes
Fixed Size 2263936 bytes
Variable Size 9663677568 bytes
Database Buffers 8.4289E+10 bytes
Redo Buffers 112766976 bytes
Database mounted.
SQL> flashback database to restore point before_201712151111;
Flashback complete.
SQL> alter database open resetlogs;
Database altered.

此时主库scott.t已不存在：
SQL> select from scott.t;
select from scott.t

• ERROR at line 1:
  ORA-00942: table or view does not exist
  此时从库的scott.依旧存在，主备同步终止
  解决方案：在主库创建快照时间点，从库自动停止应用日志，等主库闪回后，重新应用日志即可。
  如果已经做了上述操作，从库可以选择重建
  ALTER DATABASE REGISTER LOGFILE '/xx/xx/archive.dbf';

  c.闪回snapshot standby

  此功能在11GR2非常实用，可自动创建闪回点、开启闪回日志，可完成线上数据测试后，然后做数据库闪回恢复主备关系

SQL> set line 200;
SQL> set pagesize 2000;
SQL> select database_role,flashback_on from v$database;

DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON

PHYSICAL STANDBY READ ONLY testdbms NO

SQL> ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;

Database altered.

SQL> select database_role,flashback_on from v$database;

DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON

SNAPSHOT STANDBY MOUNTED testdbms RESTORE POINT ONLY

SQL> alter database open;

Database altered.

SQL> select open_mode from v$database;

OPEN_MODE

READ WRITE

此时备库操作：
SQL> select * from scott.emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

SMITH CLERK 7902 1980-12-17 00:00:00 800 20
ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
KING PRESIDENT 1981-11-17 00:00:00 5000 10
TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
JAMES CLERK 7698 1981-12-03 00:00:00 950 30
FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
rows selected.

SQL> truncate table scott.emp;

Table truncated.

主库操作：
SQL> create table scott.t as select * from scott.dept;

Table created.

SQL> select * from scott.t;

DEPTNO DNAME LOC ADDR

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO

备库恢复到物理standby
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.

Total System Global Area 9.4067E+10 bytes
Fixed Size 2263936 bytes
Variable Size 9663677568 bytes
Database Buffers 8.4289E+10 bytes
Redo Buffers 112766976 bytes
Database mounted.
SQL> ALTER DATABASE CONVERT TO PHYSICAL STANDBY;

Database altered.
SQL> shutdown immediate;
ORA-01507: database not mounted

ORACLE instance shut down.
SQL> startup ;
ORACLE instance started.

Total System Global Area 9.4067E+10 bytes
Fixed Size 2263936 bytes
Variable Size 9663677568 bytes
Database Buffers 8.4289E+10 bytes
Redo Buffers 112766976 bytes
Database mounted.
Database opened.

此时备库的数据已经恢复到转变snapshot standby时间点

SQL> select database_role,flashback_on from v$database;

DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON

PHYSICAL STANDBY READ ONLY testdbms NO

SQL> select * from scott.emp;

EMPNO ENAME JOB MGR HIREDATE SAL COMM DEPTNO

SMITH CLERK 7902 1980-12-17 00:00:00 800 20
ALLEN SALESMAN 7698 1981-02-20 00:00:00 1600 300 30
WARD SALESMAN 7698 1981-02-22 00:00:00 1250 500 30
JONES MANAGER 7839 1981-04-02 00:00:00 2975 20
MARTIN SALESMAN 7698 1981-09-28 00:00:00 1250 1400 30
BLAKE MANAGER 7839 1981-05-01 00:00:00 2850 30
CLARK MANAGER 7839 1981-06-09 00:00:00 2450 10
SCOTT ANALYST 7566 1987-04-19 00:00:00 3000 20
KING PRESIDENT 1981-11-17 00:00:00 5000 10
TURNER SALESMAN 7698 1981-09-08 00:00:00 1500 0 30
ADAMS CLERK 7788 1987-05-23 00:00:00 1100 20
JAMES CLERK 7698 1981-12-03 00:00:00 950 30
FORD ANALYST 7566 1981-12-03 00:00:00 3000 20
MILLER CLERK 7782 1982-01-23 00:00:00 1300 10
rows selected.

SQL> alter database recover managed standby database using current logfile disconnect;

Database altered.

SQL> select * from scott.t;

DEPTNO DNAME LOC ADDR

ACCOUNTING NEW YORK
RESEARCH DALLAS
SALES CHICAGO

SQL> select database_role,flashback_on from v$database;

DATABASE_ROLE OPEN_MODE DB_UNIQUE_NAME FLASHBACK_ON

PHYSICAL STANDBY READ ONLY WITH APPLY testdbms NO

(5)闪回归档(增加、修改、重命名、删除表的列、truncate表、修改表的约束、以及修改分区表的分区规范)

3、闪回注意事项

(1)数据库闪回需要在mounted下进行，并且open时需要使用resetlogs

(2)闪回DROP只能用于非系统表空间和本地管理的表空间，外键约束无法恢复，对方覆盖、重命名需注意

(3)表DROP，对应的物化视图会被彻底删除，物化视图不会存放在recyclebin里

(4)闪回表，如果在做过dml，然后进行了表结构修改、truncate等DDL操作，新增/删除结构无法做闪回

(5)闪回归档，必须在assm管理tablespace和undo auto管理下进行

(6)注意闪回区管理，防止磁盘爆满，闪回区空间不足等

(7)主库做库的闪回，会影响备库，需要重新同步

(8)snapshot standby 不支持最高保护模式

三、备注

1、相关数据字典

V$FLASHBACK_DATABASE_LOG ##查看数据库可闪回的时间点/SCN等信息 V$flashback_database_stat ##查看闪回日志空间记录信息

2、常用查询语句

(1)查看数据库状态

NAME OPEN_MODE DATABASE_ROLE CURRENT_SCN FLASHBACK_ON

TESTDB READ WRITE PRIMARY 16812246 YES

(2)获取当前数据库的系统时间和SCN

SYSDT SCN

2017-12-14 14:28:33 16813234

(3)查看数据库可恢复的时间点

OLDEST_FLASHBACK_SCN OLDEST_FLASHBACK_TI RETENTION_TARGET FLASHBACK_SIZE ESTIMATED_FLASHBACK_SIZE

16801523 2017-12-14 11:35:05 4320 104857600 244113408

(4)查看闪回日志空间情况

(5)SCN和timestamp装换关系查询

(6)查看闪回restore_point

(7)闪回语句

a.闪回数据库

b.闪回DROP

其中table_name可以是删除表名称，也可以是别名

c.闪回表

d.闪回查询

e.闪回快照

(7)闪回空间爆满问题处理

请参照

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