闪回数据库的简单介绍
闪回数据库方法可以用sqlplus，也可以用RMAN执行：
SQL> FLASHBACK DATABASE TO TIMESTAMP(''); --(基于时间点)
SQL> FLASHBACK DATABASE TO SCN ; --(基于SCN)
SQL> FLASHBACK DATABASE TO RESTORE POINT ; --(基于sestore point ，创建命令create restore point 名称)
RMAN> FLASHBACK DATABASE TO TIME = "TO_DATE('2009-05-27 16:00:00', 'YYYY-MM-DD HH24:MI:SS')";--(基于时间点)
RMAN> FLASHBACK DATABASE TO SCN=23565; --(基于SCN)
RMAN> FLASHBACK DATABASE TO SEQUENCE=223 THREAD=1; --（序列号，可用list incarnation of database 查看当前sequence)
上述两种方法都可以实现flashback database需要注意的是操作完成后使用命令打开数据库alter database open resetlogs
下面来演示下基于时间点的闪回数据库实验：
1.查看当前归档
SQL> archive log list
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 25
Next log sequence to archive 27
Current log sequence 27
2.查看下闪回数据库打开没，如果没打开使用alter database flashback on命令打开
SQL> select flashback_on from v_$database;
FLASHBACK_ON
------------------
YES
3.先查询当前时间
SQL> select to_char(sysdate,'yyyy-mm-dd:hh34:mi:ss') from dual;
TO_CHAR(SYSDATE,'YY
-------------------
2017-07-17:16:16:45
4.切换HR用 ，用HR建个表TMP717并 插入一行数据，接着把表删除（加上PURGE），用DBA用户切换日志
SQL> conn hr/123456
Connected.
SQL> create table tmp717 (cons_no varchar2(10));
Table created.
SQL> insert into tmp717 values('1');
1 row created.
SQL> commit;
Commit complete.
SQL> select to_char(sysdate,'yyyy-mm-dd:hh34:mi:ss') from dual;
TO_CHAR(SYSDATE,'YY
-------------------
2017-07-17:16:20:47
SQL> drop table tmp717 purge
2 ;
Table dropped.
SQL> conn / as sysdba
Connected.
SQL> alter system switch logfile;
System altered.
SQL> archive log list
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 26
Next log sequence to archive 28
Current log sequence 28
（当前日志变成28）
5.关闭数据库，启动到MOUNT状态（闪回数据库必须的操作）
SQL> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.
Total System Global Area 820236288 bytes
Fixed Size 1339628 bytes
Variable Size 549457684 bytes
Database Buffers 264241152 bytes
Redo Buffers 5197824 bytes
Database mounted.
SQL> exit
6.打开RMAN进行闪回操作
[oracle@station4 ~]$ rman target /
Recovery Manager: Release 11.2.0.1.0 - Production on Mon Jul 17 16:31:13 2017
Copyright (c) 1982, 2009, Oracle and/or its affiliates. All rights reserved.
connected to target database: ORCL (DBID=1359978017, not open)
RMAN> list incarnation of database ;--（先查看下当前化身）
List of Database Incarnations
DB Key Inc Key DB Name DB ID STATUS Reset SCN Reset Time
------- ------- -------- ---------------- --- ---------- ----------
1 1 ORCL 1359978017 PARENT 1 13-AUG-09
2 2 ORCL 1359978017 CURRENT 754488 22-NOV-13
RMAN> run {
2> sql "alter session set nls_date_format=''YYYY-MM-DD:HH24:MI:SS''";
3> set until time '2017-07-17:16:20:47';
4> restore database;
5> recover database;}
7.用RESETLOGS打开数据库，并查询表还原成功
SQL> alter database open resetlogs;
Database altered.
SQL> select * from hr.tmp717;
CONS_NO
----------
1
8.重新查看化身
RMAN> list incarnation of database;
List of Database Incarnations
DB Key Inc Key DB Name DB ID STATUS Reset SCN Reset Time
------- ------- -------- ---------------- --- ---------- ----------
1 1 ORCL 1359978017 PARENT 1 13-AUG-09
2 2 ORCL 1359978017 PARENT 754488 22-NOV-13
3 3 ORCL 1359978017 CURRENT 1083685 17-JUL-17
上述实验也可以用SQL> FLASHBACK DATABASE TO TIMESTAMP('2017-07-17:16:20:47'); 操作结果是一样的
实验中看出化身了一个，当前化身号是1083685，并且删除的表还原回来了，表示成功执行。