时间：2021-07-01 10:21:17 帮助过：40人阅读
--- 说明闪回数据库 --- 使用闪回表将表内容还原到过去的特定时间点 --- 从删除表中进行恢复 --- 使用闪回查询查看截止到任一时间点的数据库内容 --- 使用闪回版本查询查看某一行在一段时间内的各个版本 --- 使用闪回事务查询查看事务处理历史记录或行 优点
--- 说明闪回数据库
--- 使用闪回表将表内容还原到过去的特定时间点
--- 从删除表中进行恢复
--- 使用闪回查询查看截止到任一时间点的数据库内容
--- 使用闪回版本查询查看某一行在一段时间内的各个版本
--- 使用闪回事务查询查看事务处理历史记录或行
优点：
闪回技术由于只能处理更改数据，所以从根本上改变了恢复技术。使用这个技术时，从错误中恢复花费的时间等于制造错误所花费的时间。当闪回技术使用时，它与介质恢复相比，在易用性、可用性和还原时间方面有明显的优势。
闪回数据库使用闪回日志执行闪回。闪回删除使用回收站。其他所有功能都使用还原数据。
闪回时间浏览
闪回技术提供的功能可用于查询方案对象的过去版本、查询历史记录数据以及执行更改分析。每个事务处理在逻辑上都会生成新版本数据库。使用闪回技术，可通过浏览这些版本来查找错误以及原因。
· 闪回查询：查询特定时间点的所有数据。
· 闪回版本查询：查看两个时间之间行的所有版本已经更改了行的事务处理。
· 闪回事务处理查询：查看事务处理做的所有更改。
使用闪回查询功能时，可以对自特定时间起的数据库执行查询。通过使用select语句的 as of 子句，可指定要查看其数据的时间戳。这有助于分析数据差异。
实验一：闪回查询
实验一：闪回查询：as of timestamp
SYS@ORCL>conn tyger/tyger
Connected.
TYGER@ORCL>create table fb_query as select * from scott.dept;
Table created.
TYGER@ORCL>select * from fb_query;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
TYGER@ORCL>set time on;
09:51:36 TYGER@ORCL>delete fb_query where deptno=10;
1 row deleted.
09:51:53 TYGER@ORCL>commit;
Commit complete.
09:51:57 TYGER@ORCL>select * from fb_query;
DEPTNO DNAME LOC
---------- -------------- -------------
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
09:52:06 TYGER@ORCL>select * from fb_query as of timestamp sysdate-1/1440;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
实验二：闪回查询应用
10:25:04 TYGER@ORCL>drop table fb_tyger purge;
Table dropped.
10:25:10 TYGER@ORCL>create table fb_tyger as select * from scott.dept;
Table created.
10:25:33 TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
10:25:44 TYGER@ORCL>select sysdate from dual;
SYSDATE
---------
14-MAR-14
10:26:02 TYGER@ORCL>alter session set nls_date_format='yyyy-mm-dd hh24:mi:ss';
Session altered.
10:26:30 TYGER@ORCL>select sysdate from dual;
SYSDATE
-------------------
2014-03-14 10:26:38
10:26:38 TYGER@ORCL>update fb_tyger set dname='';
4 rows updated.
10:26:51 TYGER@ORCL>commit;
Commit complete.
10:26:54 TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
10 NEW YORK
20 DALLAS
30 CHICAGO
40 BOSTON
10:27:12 TYGER@ORCL>select * from fb_tyger as of timestamp to_timestamp('2014-03-14 10:26:38','yyyy-mm-dd hh24:mi:ss');
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
此处遇到错误：
ERROR at line 1:
ORA-01466: unable to read data - table definition has changed
参考文档：
10:29:21 TYGER@ORCL>select * from fb_tyger as of timestamp sysdate-3/1440;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
10:29:35 TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
10 NEW YORK
20 DALLAS
30 CHICAGO
40 BOSTON
10:46:22 TYGER@ORCL>set time off
TYGER@ORCL>update fb_tyger t
2 set dname =
3 (select dname from fb_tyger as of timestamp
4 to_timestamp('2014-03-14 10:26:38','yyyy-mm-dd hh24:mi:ss')
5 where t.deptno=fb_tyger.deptno);
4 rows updated.
TYGER@ORCL>commit;
Commit complete.
TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
实验三：闪回查询 as of scn
TYGER@ORCL>conn / as sysdba
Connected.
SYS@ORCL>grant execute on dbms_flashback to tyger;
Grant succeeded.
TYGER@ORCL>select dbms_flashback.get_system_change_number from dual;
GET_SYSTEM_CHANGE_NUMBER
------------------------
1107246
TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
TYGER@ORCL>delete fb_tyger where deptno<=30;
3 rows deleted.
TYGER@ORCL>commit;
Commit complete.
TYGER@ORCL>select * from fb_tyger;
DEPTNO DNAME LOC
---------- -------------- -------------
40 OPERATIONS BOSTON
TYGER@ORCL>select * from fb_tyger as of scn 1107246;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
实验四：利用PL/SQL包dbms_flashback
语法：
· 会话启用闪回指定时间：
DBMS_FLASHBACK.ENABLE_AT_TIME(query_time IN TIMESTAMP);
· 会话启用闪回指定SCN：
DBMS_FLASHBACK.ENABLE_AT_SYSTEM_CHANGE_NUMBER(query_scn IN NUMBER);
· 关闭闪回：
DBMS_FLASHBACK.DISABLE;
TYGER@ORCL>conn / as sysdba
Connected.
SYS@ORCL>grant execute on dbms_flashback to tyger;
Grant succeeded.
SYS@ORCL>conn tyger/tyger
Connected.
TYGER@ORCL>
TYGER@ORCL>
TYGER@ORCL>
TYGER@ORCL>create table fb_query1 as select * from scott.dept;
Table created.
TYGER@ORCL>create table fb_query2 as select * from scott.dept;
Table created.
TYGER@ORCL>commit;
Commit complete.
TYGER@ORCL>select * from fb_query1;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
TYGER@ORCL>select * from fb_query2;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
TYGER@ORCL>set time on;
11:03:38 TYGER@ORCL>update fb_query1 set loc='';
4 rows updated.
11:03:52 TYGER@ORCL>commit;
Commit complete.
11:03:54 TYGER@ORCL>update fb_query2 set dname='';
4 rows updated.
11:04:14 TYGER@ORCL>commit;
Commit complete.
11:04:15 TYGER@ORCL>
11:04:15 TYGER@ORCL>select * from fb_query1;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING
20 RESEARCH
30 SALES
40 OPERATIONS
11:04:23 TYGER@ORCL>select * from fb_query2;
DEPTNO DNAME LOC
---------- -------------- -------------
10 NEW YORK
20 DALLAS
30 CHICAGO
40 BOSTON
// 闪回定位到5分钟前，此时若访问sysdate等时间函数，那么返回的是当前值而非5分钟之前。
11:04:30 TYGER@ORCL>exec dbms_flashback.enable_at_time(sysdate-5/1440);
PL/SQL procedure successfully completed.
11:05:09 TYGER@ORCL>select * from fb_query1;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
11:05:29 TYGER@ORCL>select * from fb_query2;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING NEW YORK
20 RESEARCH DALLAS
30 SALES CHICAGO
40 OPERATIONS BOSTON
//处于闪回会话模式时，不允许执行DML 、 DDL 操作
11:05:45 TYGER@ORCL>update fb_query1 set dname='';
update fb_query1 set dname=''
*
ERROR at line 1:
ORA-08182: operation not supported while in Flashback mode
11:05:59 TYGER@ORCL>exec dbms_flashback.disable;
PL/SQL procedure successfully completed.
11:06:18 TYGER@ORCL>select * from fb_query1;
DEPTNO DNAME LOC
---------- -------------- -------------
10 ACCOUNTING
20 RESEARCH
30 SALES
40 OPERATIONS
11:06:30 TYGER@ORCL>select * from fb_query2;
DEPTNO DNAME LOC
---------- -------------- -------------
10 NEW YORK
20 DALLAS
30 CHICAGO
40 BOSTON
11:06:37 TYGER@ORCL>update fb_query1 set dname='' where deptno=10;
1 row updated.
11:07:10 TYGER@ORCL>select * from fb_query1;
DEPTNO DNAME LOC
---------- -------------- -------------
10
20 RESEARCH
30 SALES
40 OPERATIONS
// sys 用户不允许使用dbms_flashback 包
11:07:20 TYGER@ORCL>conn / as sysdba
Connected.
11:07:35 SYS@ORCL>set time off
SYS@ORCL>exec dbms_flashback.enable_at_time(sysdate-5/1440);
BEGIN dbms_flashback.enable_at_time(sysdate-5/1440); END;
*
ERROR at line 1:
ORA-08185: Flashback not supported for user SYS
ORA-06512: at "SYS.DBMS_FLASHBACK", line 3
ORA-06512: at line 1
实验二：闪回版本
---通过闪回版本可审计表行，检索影响行的事务处理的有关信息。然后可使用返回的事务处理标识符来执行事务处理挖掘(通过使用LogMiner)或执行闪回版本查询。