ORACLE 10g FLASHBACK (二)
关于ORACLE FLASHBACK特性
从9i版本开始，Oracle通过DBMS_FLASHBACK包提供flashback query功能,Oracle 10g版本进一步扩展了flashback功能，利用flashabck我们可以做到flashback query,flashback table,flashback database等操作.
flashback table与9i的flashback query相似,但是说明的是，flashback table不等于flashback query，所谓query，仅仅是查询以前的一个快照点而已，并不改变当前表的状态，而flashback table不一样，将改变当前表及附属对象一起回到以前的时间点。
其实9i的flashback query在10g中也有了新的变化，10g中可以简单的利用以下语句实现flashback query，而不再需要象9i那样需要调用DBMS_FLASHBACK包。
SELECT * FROM TABLENAME AS OF TIMESTAMP
TO_TIMESTAMP('2010-08-04 09:30:00', 'YYYY-MM-DD HH:MI:SS')
WHERE ……;
提示：如果需要flashback一个表，需要保证
需要有flashback any table的系统权限或者是该表的flashback对象权限。
需要有该表的SELECT, INSERT, DELETE, ALTER权限
必须保证该表ROW MOVEMENT
sys用户不能使用回收站闪回表工作
闪回恢复已经在上一节设置好，下面我们开始做闪回例子
--测试用例环境 DB:10.2.0.4 OS:rhel5.4
1.Flashback Query
1).原理:Flashback Query通过Undo数据，利用一致读的方法来查找用户需要的数据.
2).使用范围:查找指定时间点被删除(delete,被update)的数据
3).注意点:1).闪回时间受参数undo_retention影响 2).闪回时间受undo表空间大小影响 3).查询之前的快照点，并不改变当前表的状态
4).语法:1).select ... from table_name as of timestamp ... 2).select ... from table_name as of scn ...
5).举例：
SQL>create table test(id number,scn number,time varchar2(20));
Table created.
SQL>begin
2 for i in 1..20
3 loop
4 insert into test values(i,dbms_flashback.get_system_change_number(),to_char(sysdate,'yyyy-mm-dd hh24:mi:ss')); --插入scn和sysdate为了后面查询方便明了
5 commit; --如果不加commit 会造成scn都是一样的
6 dbms_lock.sleep(3); --估计加大插入间隔
7 end loop;
8 end;
9 /
PL/SQL procedure successfully completed.
SQL>select * from test;
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
16 1648274 2010-08-12 11:11:37
17 1648276 2010-08-12 11:11:40
18 1648278 2010-08-12 11:11:43
19 1648280 2010-08-12 11:11:46
20 1648282 2010-08-12 11:11:49
20 rows selected.
SQL>select * from test as of scn 1648247; --根据自己实际数据，我选择的是第3条数据
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
SQL>select * from test as of timestamp to_timestamp('2010-08-12 11:10:58','yyyy-mm-dd hh24:mi:ss'); --根据自己实际数据，同样是第3条数据
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
--从上面例子也可以看出scn和timestamp并不是完全对应的.在实际案例中我们往往忽略这些微小差别.
2.Flashback Table
1).原理:Flashback Table也是利用Undo数据来恢复对象到指定时间点
2).使用范围:恢复当前表及其相关对象到某个时间点
3).注意点:1).闪回时间受参数undo_retention影响 2).闪回时间受undo表空间大小影响 3).和flashback query有差别，恢复表到以前的时间点 4).flashback之前要先允许row movement
4).语法:1).flashback table table_name to timestamp .... 2).flash table table_name to scn ... 3).flashback table table_name to timestamp ... enable triggers.
5).举例
SQL>select * from test;
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
16 1648274 2010-08-12 11:11:37
17 1648276 2010-08-12 11:11:40
18 1648278 2010-08-12 11:11:43
19 1648280 2010-08-12 11:11:46
20 1648282 2010-08-12 11:11:49
20 rows selected.
SQL>alter table test enable row movement; --允许数据库移动列
Table altered.
SQL>flashback table test to timestamp to_timestamp('2010-08-12 11:11:40','yyyy-mm-dd hh24:mi:ss'); --flashback到某一时间点
Flashback complete.
SQL>select * from test; --表的数据已经改变
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
16 1648274 2010-08-12 11:11:37
17 1648276 2010-08-12 11:11:40
17 rows selected.
SQL>flashback table test to scn 1648274;
Flashback complete.
SQL>select * from test;
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
15 rows selected.
3.Flashback Drop(RecycleBin)
1).原理:利用类似于windows的回收站来支持flashback drop（当表被删除时，数据库仅仅修改一下相关对象的名字，flashback过程相当于重新命名回来而已）
2).使用范围：恢复被误删除的表极其相关对象
3).注意点:1).闪回主要看回收站大小 2).truncate对象不能被flashback
4).语法:1).flashback table table_name to before drop 2).flashback table table_name to before drop rename to new_table_name;
5).举例
SQL>drop table test; --首先drop表
Table dropped.
SQL>select * from test; --表已经不存在
select * from test
*
ERROR at line 1:
ORA-00942: table or view does not exist
SQL>flashback table test to before drop; --通过flashback drop恢复表
Flashback complete.
SQL>select * from test; --表已经恢复
ID SCN TIME
---------- ---------- ----------------------------------------
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
15 rows selected.
4.Flashback Version Query
1).原理:利用Undo来查看多版本
2).使用范围：查看行改变情况
3).注意点:1).闪回时间受参数undo_retention影响 2).闪回时间受undo表空间大小影响 3).查询行改变情况，并不改变当前表的状态
4).语法:1).select * from table_name versions between timestamp ... and ... 2).select * from table_name versions between scn ... and ...
5).举例
--我们可能用到的伪劣:versions_starttime,versions_startscn,versions_endscn,versions_endtime,versions_xid,versions_operation这些伪列性质和rownum等是一样的
SQL>delete from test where scn >1648261;
5 rows deleted.
SQL>commit;
SQL>column VERSIONS_STARTTIME format a25;
SQL> select versions_starttime,versions_operation,id ,scn,time from jane.t versions between timestamp to_timestamp('
2010-08-12 11:50:00','yyyy-mm-dd hh24:mi:ss') and maxvalue order by versions_starttime,id;
VERSIONS_STARTTIME VE ID SCN TIME
------------------------- -- ---------- ---------- ----------------------------------------
12-AUG-10 11.50.12 AM D 11 1648263 2010-08-12 11:11:22
12-AUG-10 11.50.12 AM D 12 1648265 2010-08-12 11:11:25
12-AUG-10 11.50.12 AM D 13 1648267 2010-08-12 11:11:28
12-AUG-10 11.50.12 AM D 14 1648269 2010-08-12 11:11:31
12-AUG-10 11.50.12 AM D 15 1648271 2010-08-12 11:11:34
1 1648243 2010-08-12 11:10:52
2 1648245 2010-08-12 11:10:55
3 1648247 2010-08-12 11:10:58
4 1648249 2010-08-12 11:11:01
5 1648251 2010-08-12 11:11:04
6 1648253 2010-08-12 11:11:07
7 1648255 2010-08-12 11:11:10
8 1648257 2010-08-12 11:11:13
9 1648259 2010-08-12 11:11:16
10 1648261 2010-08-12 11:11:19
11 1648263 2010-08-12 11:11:22
12 1648265 2010-08-12 11:11:25
13 1648267 2010-08-12 11:11:28
14 1648269 2010-08-12 11:11:31
15 1648271 2010-08-12 11:11:34
20 rows selected.
--从上面信息可以看出我们在“12-AUG-09 11.50.12 AM ”时间做了D（删除）操作，删除的数据是id在11和15之间的.
5.Flashback Database
数据库可以通过flashback log来回到之前的某个时间点.
SQL>flashback database to timestamp to_timestamp('2010-08-12 23:33:34','yyyy-mm-dd hh24:mi:ss');
Flashback complete.
SQL>alter database open read only;
Database altered.
SQL> select count(*) from test;
COUNT(*)
----------
20
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.
Total System Global Area 171966464 bytes
Fixed Size 2082496 bytes
Variable Size 125831488 bytes
Database Buffers 37748736 bytes
Redo Buffers 6303744 bytes
Database mounted.
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open
--一旦resetlogs之后，就再也不能flashback database 到resetlogs之前的状态了，所以之前用open read only检查一下是否flashback 成功了。
SQL>alter database open resetlogs;
Database altered.
SQL> select count(*) from test;
COUNT(*)
----------
22
//通过v$flash_recovery_area_usage视图可以查到闪回区的使用情况。
//通过v$flashback_database_log视图可以查到flashback database能恢复到最早的时间和SCN号。