闪回数据库实验总结-MySQL 튜토리얼-php.cn

闪回数据库概念： 10G新增功能，在启用flashback database功能后，数据库会定期将发生变化的数据块的前镜像写入闪回日志的日志文件中，在进行数据库闪回时，这些数据块可以直接复制回来以满足数据库的恢复需要。 REDO LOG可以用来辅助数据恢复到更精确时间

闪回数据库概念：

10G新增功能，在启用flashback database功能后，数据库会定期将发生变化的数据块的前镜像写入闪回日志的日志文件中，

在进行数据库闪回时，这些数据块可以直接复制回来以满足数据库的恢复需要。
REDO LOG可以用来辅助数据恢复到更精确时间点，可以缩短恢复时间。
闪回数据库的日志文件由recovery writer RVWR进程写入
闪回日志文件由RVWR进程在闪回恢复区中自动创建和维护。
闪回数据库特性默认是关闭，需要在MOUNT状态打开。
闪回时可将无关的表空间暂时OFFLINE以加快恢复速度,只将SYSTEM UNDO 及所要闪回的数据对应的表空间在线即可。

不能使用闪回数据库的场景：

数据文件物理损坏--只用进行物理恢复了
数据文件shrink
使用备份的控制文件--或者重建了控制文件，因为闪回日志信息记录在控制文件中
表空间删除--
想闪回到比闪回日志中最小SCN更早的时间点--

如删除用户，可以先闪回到删除前，READ ONLY模式打开，然后EXPDP导出被删除用户。
完全恢复数据库，READ WRITE打开，再将用户导入。

总结一下开启闪回数据库功能简要步骤：
1.重启数据库到MOUNT状态-startup mount;
2.打开归档模式-alter database archivelog; 非归档时执行打开闪回数据库将报错：ORA-38707: Media recovery is not enabled.
3.设置闪回区域--需要提前在OS中创建好目录并指定大小- 未指定或指定空间不足报：ORA-38709: Recovery Area is not enabled.ORA-38708: not enough space for first flashback database log file
alter system set db_recovery_file_dest_size=2g;
alter system set db_recovery_file_dest='/backup/flashback_area';
4.打开数据库，查询归档模式-archive log list; 并查询V$DATABASE.FLASHBACK_ON字段的状态，

下面实验打开闪回数据库功能，并实际进行一次闪回数据库操作来恢复数据。

1.查看数据库归档状态并打开闪回数据库功能

22:08:49 SQL> conn / as sysdba
Connected.
22:08:54 SQL> archive log list;
Database log mode             Archive Mode
Automatic archival          Enabled
Archive destination          /u01/app/oracle/archbys001/
Oldest online log sequence    46
Next log sequence to archive 48
Current log sequence          48

如未打开归档，则报以下错误：

SYS@ bys3>alter database noarchivelog;
Database altered.
SYS@ bys3>alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38707: Media recovery is not enabled.

查看闪回状态，默认是NO，没打开。
22:08:56 SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
NO
22:09:18 SQL> host
Filesystem          Size  Used Avail Use% Mounted on
/dev/sda2             19G  9.2G  8.9G  51% /
/dev/sda1             99M 21M 74M  22% /boot
tmpfs                3.0G  484M  2.6G  16% /dev/shm
/dev/sda5          4.6G  1.4G  3.1G  31% /backup
[oracle@oel-01 ~]$ cd /backup
[oracle@oel-01 backup]$mkdir flashback_area
[oracle@oel-01 backup]$ ls
flashback_area
full
lost+found
[oracle@oel-01 backup]$ exit
exit
手动指定一下闪回区的大小和目录所在，可以使用默认值。
22:10:53 SQL> alter system set db_recovery_file_dest_size=1g;
System altered.
22:11:47 SQL> alter system set db_recovery_file_dest='/backup/flashback_area';
System altered.

如未指定闪回区，报错如下：

SYS@ bys3>alter database archivelog;
Database altered.
SYS@ bys3>alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38709: Recovery Area is not enabled.

定义一个时间上限，设置数据库能够闪回的最大时间上限，单位分钟。2880是两天。可以使用默认值。
22:11:58 SQL> alter system set db_flashback_retention_target=2880;
System altered.
22:14:12 SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
22:14:36 SQL> startup mount;
ORACLE instance started.
Total System Global Area  845348864 bytes
Fixed Size                1339796 bytes
Variable Size          583011948 bytes
Database Buffers       255852544 bytes
Redo Buffers             5144576 bytes
Database mounted.
22:20:43 SQL> show parameter db_recovery
NAME                               TYPE       VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest             string    /backup/flashback_area
db_recovery_file_dest_size          big integer 1G
打开闪回数据库特性
22:21:18 SQL> alter database flashback on;
alter database flashback on
*
ERROR at line 1:
ORA-38706: Cannot turn on FLASHBACK DATABASE logging.
ORA-38708: not enough space for first flashback database log file
22:21:32 SQL> alter system set db_recovery_file_dest_size=2g;
System altered.
22:26:22 SQL> alter database flashback on;
Database altered.
22:26:27 SQL> alter database open;
Database altered.
22:26:57 SQL> select flashback_on from v$database;
FLASHBACK_ON
------------------
YES

2.在数据库中做DDL及DML操作，并删除所建表

22:27:35 SQL> conn bys/bys
Connected.
22:34:41 SQL> create table test7 as select * from test6;
Table created.
22:37:43 SQL> select * from test7;
ABC
---------
1
2
22:37:53 SQL> select current_scn from v$database;
CURRENT_SCN
-----------
1373570
22:38:02 SQL> drop table test7;
Table dropped.
22:38:19 SQL> show recyclebin;
ORIGINAL NAME RECYCLEBIN NAME             OBJECT TYPE  DROP TIME
---------------- ------------------------------ ------------ -------------------
TEST7          BIN$39Q/PNkxLungQFXeqUARIQ==$0 TABLE    2013-06-23:22:38:18
22:38:24 SQL> purge recyclebin;
Recyclebin purged.
22:39:52 SQL> show recyclebin;
22:39:54 SQL> select oldest_flashback_scn from v$flashback_database_log;
OLDEST_FLASHBACK_SCN
--------------------
         1373161
22:40:28 SQL> ALTER SESSION SET nls_date_format = 'DD-MON-YYYY HH24:MI:SS';
Session altered.
查询最早的SCN对应的时间---我这里是上面打开闪回数据库特性的时间。
也可以从OLDEST_FLASHBACK_SCN列查最早SCN
22:40:35 SQL> SELECT oldest_flashback_time FROM v$flashback_database_log;
OLDEST_FLASHBACK_TIM
--------------------

23-JUN-2013 22:26:27

3.重启数据库到MOUNT状态进行闪回数据库操作

22:42:19 SQL> shutdown immediate;
ORA-01031: insufficient privileges
22:43:00 SQL> conn / as sysdba
Connected.
22:43:05 SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
22:43:16 SQL> startup mount;
ORACLE instance started.
Total System Global Area  845348864 bytes
Fixed Size                1339796 bytes
Variable Size          583011948 bytes
Database Buffers       255852544 bytes
Redo Buffers             5144576 bytes
Database mounted.
22:49:14 SQL> ALTER SESSION SET nls_date_format = 'DD-MON-YYYY HH24:MI:SS';
Session altered.
22:49:20 SQL> select sysdate from dual;
SYSDATE
--------------------
23-JUN-2013 22:49:25
22:49:25 SQL> SELECT oldest_flashback_time FROM v$flashback_database_log;
OLDEST_FLASHBACK_TIM
--------------------
23-JUN-2013 22:26:27
22:50:38 SQL> select oldest_flashback_scn from v$flashback_database_log;
OLDEST_FLASHBACK_SCN
--------------------
         1373161
22:50:48 SQL> flashback database to scn 1373570;
Flashback complete.

下面语句是测试过可用的使用时间戳闪回，我未使用。
SQL> flashback database to timestamp to_timestamp('2013-06-26 14:05:10','yyyy-MM-dd hh24:mi:ss');
resetlogs打开之后，不能再闪回到 resetlogs之前的时间点。
22:51:53 SQL> alter database open resetlogs;
Database altered.
22:53:18 SQL> show user
USER is "SYS"

4.使用BYS用户登陆验证第2步删除表操作之前的数据是否正常

22:54:12 SQL> conn bys/bys
Connected.
22:55:13 SQL> select * from test7;
ABC
---------
1
2

补充：不确定闪回的时间或SCN是否足够使数据恢复，可以以READ ONLY方式打开数据库
即flashback database to scn 1373570;或flashback database to timestamp to_timestamp('2013-06-26 14:05:10','yyyy-MM-dd hh24:mi:ss');

然后 alter database open read only;然后查询数据看是否需要的数据已经恢复。

如果未恢复，可以继续使用flashback database to SCN/TIMESTAMP这样语句来恢复，直到恢复出需要的数据。

确定恢复出全部需用的数据后，就可以使用alter database open resetlogs;语句打开数据库了。

resetlogs打开数据库后，就不能再使用flashback回到resetlogs之前的时间点了。

增加一个强制检查点的恢复实验--可用于打PSU时刷新数据字典时

SQL> startup mount;
ORACLE instance started.

Total System Global Area 536870912 bytes
Fixed Size                  1220432 bytes
Variable Size             125829296 bytes
Database Buffers          406847488 bytes
Redo Buffers                2973696 bytes
Database mounted.

SQL> create restore point p1 guarantee flashback database;
Restore point created.

SQL> alter database open;
Database altered.
SQL> create user bys identified by bys;
User created.

SQL> grant dba to bys;
Grant succeeded.

SQL> Flashback database to restore point p1;
Flashback database to restore point p1
*
ERROR at line 1:
ORA-38757: Database must be mounted and not open to FLASHBACK.

SQL> conn bys/bys
Connected.
SQL> conn / as sysdba
Connected.
SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORACLE instance started.
Total System Global Area 536870912 bytes
Fixed Size                  1220432 bytes
Variable Size             125829296 bytes
Database Buffers          406847488 bytes
Redo Buffers                2973696 bytes
Database mounted.

SQL> Flashback database to restore point p1;
Flashback complete.
SQL> alter database open;
alter database open
*
ERROR at line 1:
ORA-01589: must use RESETLOGS or NORESETLOGS option for database open

SQL> alter database open resetlogs;
Database altered.

SQL> select username from dba_users;
USERNAME
------------------------------
OLTP_USER
OE
HR
SST
SH
TSMSYS
DIP
DBSNMP
OUTLN
SYS
SYSTEM
11 rows selected.
SQL>