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

闪回级别	闪回场景	闪回技术	对象依赖	影响数据
数据库	表截断、逻辑错误、其他多表意外事件	闪回database	闪回日志、undo	是
drop	删除表	闪回drop	回收站(recyclebin)	是
表	更新、删除、插入记录	闪回table	还原数据,undo	是
查询	当前数据和历史数据对比	闪回query	还原数据,undo	否
版本查询	比较行版本	闪回version query	还原数据,undo	否
事务查询	比较	闪回transaction query	还原数据,undo	否
归档	ddl、dml	闪回archive	归档日志	是

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

sql> archive log list;
database log mode archive mode
automatic archival enabled
archive destination /home/u01/app/oracle/oradata/testdb/arch
oldest online log sequence 844
next log sequence to archive 846
current log sequence 846

##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

sql> select flashback_on from v$database;
flashback_on
------------------
no

(3)开启闪回

a.开启归档

mount状态：alter database archivelog;

b.设置闪回区

sql> alter system set db_recovery_file_dest='/home/u01/app/oracle/fast_recovery_area' scope=both;
system altered.
sql> alter system set db_recovery_file_dest_size=60g scope=both;
system altered.
sql> alter system set db_flashback_retention_target=4320 scope=both;
system altered. 

c.开启flashback (10g在mount开启)

sql> alter database flashback on;
database altered.

(4)确定闪回开启

sql> select flashback_on from v$database;
flashback_on
------------------
yes 

(5)关闭闪回

sql> alter database flashback off;
database altered.

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。

sql> select * from scott.dept;
deptno dname loc
---------- -------------- -------------
accounting new york
research dallas
sales chicago
operations boston
sql> delete from scott.dept where deptno=40;
row deleted.
sql> commit;
commit complete.
sql> select * from scott.dept as of timestamp sysdate-10/1440;

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> flashback table scott.dept to timestamp to_timestamp('2017-12-14 16:20:00','yyyy-mm-dd hh24:mi:ss');
flashback table scott.dept to timestamp to_timestamp('2017-12-14 16:20:00','yyyy-mm-dd hh24:mi:ss')
error at line 1:
ora-08189: cannot flashback the table because row movement is not enabled

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：

sql> select * from t ;

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。

sql> show recyclebin;
original name recyclebin name object type drop time
---------------- ------------------------------ ------------ -------------------
t bin$yeh2qcvddjlguxyagqpnvq==$0 table 2017-12-14:15:07:54
t bin$yeh2qcvcdjlguxyagqpnvq==$0 table 2017-12-14:15:07:27
sql> flashback table "bin$yeh2qcvcdjlguxyagqpnvq==$0" to before drop ;
flashback complete.
sql> show recyclebin;
original name recyclebin name object type drop time
---------------- ------------------------------ ------------ -------------------
t bin$yeh2qcvddjlguxyagqpnvq==$0 table 2017-12-14:15:07:54
sql> flashback table t to before drop rename to tt;
flashback complete.

(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

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.
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

sql> select * from scott.dept;

  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

select scn, storage_size ,to_char(time,'yyyy-mm-dd hh24:mi:ss') time,name from v$restore_point;
select database_role,open_mode,db_unique_name,flashback_on from v$database;

sql> set line 200;
sql> set pagesize 2000;
sql> select database_role,open_mode,db_unique_name,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,open_mode,db_unique_name,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,open_mode,db_unique_name,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,open_mode,db_unique_name,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

sql> select name,open_mode ,database_role,current_scn,flashback_on from v$database;

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

sql> select to_char(systimestamp,'yyyy-mm-dd hh24:mi:ss') as sysdt , dbms_flashback.get_system_change_number scn from dual;

sysdt scn
------------------- ----------
2017-12-14 14:28:33 16813234

(3)查看数据库可恢复的时间点

sql> select * from v$flashback_database_log;

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

sql> select * from v$flashback_database_stat;
begin_time end_time flashback_data db_data redo_data estimated_flashback_size
------------------- ------------------- -------------- ---------- ---------- ------------------------
2017-12-14 14:34:53 2017-12-14 14:56:43 1703936 9977856 1487872 0  

(5)scn和timestamp装换关系查询

select scn,to_char(time_dp,'yyyy-mm-dd hh24:mi:ss')from sys.smon_scn_time;

(6)查看闪回restore_point

select scn, storage_size ,to_char(time,'yyyy-mm-dd hh24:mi:ss') time,name from v$restore_point;

(7)闪回语句

a.闪回数据库

flashback database to timestamp to_timestamp('2017-12-14 14:28:33','yyyy-mm-dd hh24:mi:ss');;
flashback database to scn 16813234;

b.闪回drop

其中table_name可以是删除表名称，也可以是别名

flashback table table_name to before drop;
flashback table table_name to before drop rename to table_name_new;

c.闪回表

flashback table table_name to scn scn_number;
flashback table table_name to timestamp to_timestamp('2017-12-14 14:28:33','yyyy-mm-dd hh24:mi:ss');

d.闪回查询

select * from table_name as of timestamp to_timestamp('2017-12-14 14:28:33','yyyy-mm-dd hh24:mi:ss');
select * from scott.dept as of scn 16801523;

e.闪回快照

create restore point before_201712151111 guarantee flashback database;

flashback database to restore point before_201712151111;

(7)闪回空间爆满问题处理

请参照 基于ora-19815闪回空间爆满问题的处理方法

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