20、oracle用户管理恢复

下面会一一讲解控制文件、redo文件及非归档模式、归档模式数据文件丢失的情况下，如何恢复数据？

(1)控制文件(controlfile)丢失

在做恢复实验之前，先备份好数据。

案例1、模拟一个控制文件丢失

select name from v$controlfile;

SQL> select name from v$controlfile;

NAME

--------------------------------------------------------------------------------

/u02/oracle/oradata/orcl/control01.ctl

/u02/oracle/oradata/orcl/control02.ctl

删除其中一个控制文件

rm -rf /u02/oracle/oradata/orcl/control01.ctl

alter system switch logfile;

create tablespace hello datafile '/u02/oracle/oradata/orcl/hello01.dbf';

SQL> create tablespace hello datafile '/u02/oracle/oradata/orcl/hello01.dbf';

create tablespace hello datafile '/u02/oracle/oradata/orcl/hello01.dbf'

ERROR at line 1:

ORA-00210: cannot open the specified control file

ORA-00202: control file: '/u02/oracle/oradata/orcl/control01.ctl'

ORA-27041: unable to open file

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

数据库启动不起来

SQL> startup

ORACLE instance started.

Total System Global Area 2772574208 bytes

Fixed Size 2256472 bytes

Variable Size 771752360 bytes

Database Buffers 1979711488 bytes

Redo Buffers 18853888 bytes

ORA-00205: error in identifying control file,check alert log for more info

SQL> select status from v$instance;

STATUS

------------

STARTED

查看alert log内容如下：

tail -f /u02/oracle/diag/rdbms/orcl/orcl/trace/alert_orcl.log

ORA-00210: cannot open the specified control file

ORA-00202: control file: '/u02/oracle/oradata/orcl/control01.ctl'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

Wed Aug 30 23:30:34 2017

Checker run found 1 new persistent data failures

ORA-205 signalled during: ALTER DATABASE MOUNT...

如何恢复控制文件呢？

cp /u02/oracle/oradata/orcl/control02.ctl /u02/oracle/oradata/orcl/control01.ctl

ALTER DATABASE MOUNT;

ALTER DATABASE open;

案例2、控制文件全部丢失。(前提控制文件有备份)

alter database backup controlfile to '/u02/ctlbak001';（备份）

rm -rf /u02/oracle/oradata/orcl/control01.ctl

rm -rf /u02/oracle/oradata/orcl/control02.ctl

SQL> startup

ORACLE instance started.

Total System Global Area 2772574208 bytes

Fixed Size 2256472 bytes

Variable Size 771752360 bytes

Database Buffers 1979711488 bytes

Redo Buffers 18853888 bytes

ORA-00205: error in identifying control file,check alert log for more info

ORA-00202: control file: '/u02/oracle/oradata/orcl/control02.ctl'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

ORA-00210: cannot open the specified control file

ORA-00202: control file: '/u02/oracle/oradata/orcl/control01.ctl'

如何恢复控制文件呢？

cp /u02/ctlbak001 /u02/oracle/oradata/orcl/control01.ctl

cp /u02/ctlbak001 /u02/oracle/oradata/orcl/control02.ctl

启动数据库还是报错

SQL> startup

ORACLE instance started.

Total System Global Area 2772574208 bytes

Fixed Size 2256472 bytes

Variable Size 771752360 bytes

Database Buffers 1979711488 bytes

Redo Buffers 18853888 bytes

Database mounted.

ORA-01589: must use RESETLOGS or NORESETLOGS option for database open

SQL> select GROUP#,FIRST_CHANGE#,NEXT_CHANGE# from v$log;

GROUP# FIRST_CHANGE# NEXT_CHANGE#

---------- ------------- ------------

1 1520101 1520104

3 1540267 2.8147E+14

2 1520104 1540267

继续执行如下命令：

recover database using backup controlfile;

SQL> recover database using backup controlfile;

ORA-00279: change 1540268 generated at 08/30/2017 23:34:57 needed for thread 1

ORA-00289: suggestion : /u02/arch/1_51_944544087.dbf

ORA-00280: change 1540268 for thread 1 is in sequence #51

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

auto

ORA-00308: cannot open archived log '/u02/arch/1_51_944544087.dbf'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

ORA-00308: cannot open archived log '/u02/arch/1_51_944544087.dbf'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

SQL> select GROUP#,MEMBER from v$logfile;

GROUP#

MEMBER

--------------------------------------------------------------------------------

/u02/oracle/oradata/orcl/redo03.log

/u02/oracle/oradata/orcl/redo02.log

/u02/oracle/oradata/orcl/redo01.log

通过上面分析，可以从/u02/oracle/oradata/orcl/redo03.log 恢复控制文件。

继续执行recover database using backup controlfile 命令

SQL> recover database using backup controlfile

ORA-00279: change 1540268 generated at 08/30/2017 23:34:57 needed for thread 1

ORA-00289: suggestion : /u02/arch/1_51_944544087.dbf

ORA-00280: change 1540268 for thread 1 is in sequence #51

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

/u02/oracle/oradata/orcl/redo03.log

Log applied.

Media recovery complete.

最后执行命令：

alter database open resetlogs;

搞定。

方法2：通过rman备份恢复控制文件。

下面通过rman备份控制文件来实验：

rman target /

RMAN> show all;

using target database control file instead of recovery catalog

RMAN configuration parameters for database with db_unique_name ORCL are:

CONFIGURE RETENTION POLICY TO REDUNDANCY 1; # default

CONFIGURE BACKUP OPTIMIZATION OFF; # default

CONFIGURE DEFAULT DEVICE TYPE TO DISK; # default

CONFIGURE CONTROLFILE AUTOBACKUP OFF; # default

CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F'; # default

CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET; # default

CONFIGURE DATAFILE BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default

CONFIGURE ARCHIVELOG BACKUP COPIES FOR DEVICE TYPE DISK TO 1; # default

CONFIGURE MAXSETSIZE TO UNLIMITED; # default

CONFIGURE ENCRYPTION FOR DATABASE OFF; # default

CONFIGURE ENCRYPTION ALGORITHM 'AES128'; # default

CONFIGURE COMPRESSION ALGORITHM 'BASIC' AS OF RELEASE 'DEFAULT' OPTIMIZE FOR LOAD TRUE ; # default

CONFIGURE ARCHIVELOG DELETION POLICY TO NONE; # default

CONFIGURE SNAPSHOT CONTROLFILE NAME TO '/u02/oracle/app/dbs/snapcf_orcl.f'; # default

可以通过 CONFIGURE CONTROLFILE AUTOBACKUP OFF; # default

看到rman没有自动备份控制文件。

rman手动备份控制文件

backup current controlfile;

RMAN> backup current controlfile;

Starting backup at 31-AUG-17

allocated channel: ORA_DISK_1

channel ORA_DISK_1: SID=39 device type=DISK

channel ORA_DISK_1: starting full datafile backup set

channel ORA_DISK_1: specifying datafile(s) in backup set

including current control file in backup set

channel ORA_DISK_1: starting piece 1 at 31-AUG-17

channel ORA_DISK_1: finished piece 1 at 31-AUG-17

piece handle=/u02/oracle/app/dbs/02sd9jb1_1_1 tag=TAG20170831T125145 comment=NONE

channel ORA_DISK_1: backup set complete,elapsed time: 00:00:01

Finished backup at 31-AUG-17

下面模拟删除所有控制文件

rm -rf /u02/oracle/oradata/orcl/control01.ctl

rm -rf /u02/oracle/oradata/orcl/control02.ctl

shutdown immediate;

startup;

进入rman

[oracle@oracle250 ~]$ rman target /

Recovery Manager: Release 11.2.0.4.0 - Production on Thu Aug 31 13:11:34 2017

connected to target database: ORCL (not mounted)

通过rman备份的控制文件路径恢复。

restore controlfile from '/u02/oracle/app/dbs/02sd9jb1_1_1';

RMAN> restore controlfile from '/u02/oracle/app/dbs/02sd9jb1_1_1';

Starting restore at 31-AUG-17

using target database control file instead of recovery catalog

allocated channel: ORA_DISK_1

channel ORA_DISK_1: SID=21 device type=DISK

channel ORA_DISK_1: restoring control file

channel ORA_DISK_1: restore complete,elapsed time: 00:00:03

output file name=/u02/oracle/oradata/orcl/control01.ctl

output file name=/u02/oracle/oradata/orcl/control02.ctl

Finished restore at 31-AUG-17

执行命令：

alter database mount;

alter database open;

SQL> alter database open;

alter database open

ERROR at line 1:

ORA-01589: must use RESETLOGS or NORESETLOGS option for database open

通过数据文件和控制文件的检查点信息可以看出，数据文件比控制文件的检查点要小。

col FILE for a10;

col Name for a20;

col CHECKPOINT_CHANGE for a10;

select FILE#,Name,CHECKPOINT_CHANGE# from v$datafile;

select FILE#,CHECKPOINT_CHANGE# from v$datafile_header;

继续执行recover database using backup controlfile 命令

SQL> select GROUP#,NEXT_CHANGE# from v$log;

GROUP# FIRST_CHANGE# NEXT_CHANGE#

---------- ------------- ------------

1 1540805 2.8147E+14

3 0 0

2 0 0

使用redo日志推进控制文件。

SQL> recover database using backup controlfile;

ORA-00279: change 1561276 generated at 08/31/2017 00:16:02 needed for thread 1

ORA-00289: suggestion : /u02/arch/1_1_953424962.dbf

ORA-00280: change 1561276 for thread 1 is in sequence #1

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

/u02/oracle/oradata/orcl/redo01.log

Log applied.

Media recovery complete.

最后执行命令：

alter database open resetlogs;

搞定。

注意：alter database open resetlogs; 这个命令，表示所有备份都失效了，要重新热备份哦。

方法3：通过trace恢复控制文件

问题：如果控制文件没有备份、rman也没有备份控制文件，只有备份trace文件，如何恢复控制文件呢？

首先，备份 alter database backup controlfile to trace as '/u02/ctlbak.trace';

然后模拟故障：删除控制文件：

rm -rf /u02/oracle/oradata/orcl/control01.ctl

rm -rf /u02/oracle/oradata/orcl/control02.ctl

根据trace文件重建控制文件：

CREATE CONTROLFILE REUSE DATABASE "ORCL" NORESETLOGS ARCHIVELOG

MAXLOGFILES 16

MAXLOGMEMBERS 3

MAXDATAFILES 100

MAXINSTANCES 8

MAXLOGHISTORY 292

LOGFILE

GROUP 1 '/u02/oracle/oradata/orcl/redo01.log' SIZE 50M BLOCKSIZE 512,

GROUP 2 '/u02/oracle/oradata/orcl/redo02.log' SIZE 50M BLOCKSIZE 512,

GROUP 3 '/u02/oracle/oradata/orcl/redo03.log' SIZE 50M BLOCKSIZE 512

-- STANDBY LOGFILE

DATAFILE

'/u02/oracle/oradata/orcl/system01.dbf',

'/u02/oracle/oradata/orcl/sysaux01.dbf',

'/u02/oracle/oradata/orcl/undotbs01.dbf',

'/u02/oracle/oradata/orcl/users01.dbf',

'/u02/oracle/oradata/orcl/test01.dbf',

'/u02/oracle/oradata/orcl/rrr.dbf',

'/u02/oracle/oradata/orcl/tttt.dbf',

'/u02/oracle/oradata/orcl/tttt02.dbf',

'/u02/oracle/oradata/orcl/tttt03.dbf'

CHARACTER SET AL32UTF8

Control file created.

查看数据库状态：

SQL> select status from v$instance;

STATUS

------------

MOUNTED

alter database open;

SQL> alter database open;

alter database open

ERROR at line 1:

ORA-01113: file 1 needs media recovery

ORA-01110: data file 1: '/u02/oracle/oradata/orcl/system01.dbf';

SQL> select GROUP#,SEQUENCE#,NEXT_CHANGE# from v$log;

使用redo推进控制文件。

SQL> recover database using backup controlfile;

ORA-00279: change 1562427 generated at 08/31/2017 13:44:20 needed for thread 1

ORA-00289: suggestion : /u02/arch/1_1_953472820.dbf

ORA-00280: change 1562427 for thread 1 is in sequence #1

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

/u02/oracle/oradata/orcl/redo01.log

Log applied.

Media recovery complete.

SQL> alter database open resetlogs;

Database altered.

最后也要重新备份数据库。

(2)重做日志丢失

如果丢失重做日志文件组中的某个成员，并且组中至少还有一个成员，影响如下：

不会影响实例的正常操作，

通过删除丢失的日志成员，在添加新成员的方式来恢复。

如果日志切换，该日志已经归档(不是current log)，则可以清空该日志组，然后重建丢失的日志成员。

在做实验之前，先做redo log 的多路复用。

select GROUP#,member from v$logfile;

GROUP# MEMBER

---------- --------------------------------------------------

1 /u02/oracle/oradata/orcl/redo01.log

3 /u02/oracle/oradata/orcl/redo03.log

2 /u02/oracle/oradata/orcl/redo02.log

下面多路复用。

alter database add logfile member '/u01/redo/redo01_1.log' to group 1;

alter database add logfile member '/u01/redo/redo02_1.log' to group 2;

alter database add logfile member '/u01/redo/redo03_1.log' to group 3;

alter system switch logfile;

在查询结果如下：

select GROUP#,member,status from v$logfile order by 1;

SQL> select GROUP#,status from v$logfile order by 1;

GROUP# MEMBER STATUS

---------- -------------------------------------------------- -------

1 /u02/oracle/oradata/orcl/redo01.log

1 /u01/redo/redo01_1.log

2 /u02/oracle/oradata/orcl/redo02.log

2 /u01/redo/redo02_1.log

3 /u02/oracle/oradata/orcl/redo03.log

3 /u01/redo/redo03_1.log

6 rows selected.

STATUS为空表示redo可以使用。

select a.GROUP#,a.MEMBERS,a.ARCHIVED,a.STATUS,b.MEMBER,b.STATUS from v$log a,v$logfile b where a.GROUP#=b.GROUP# order by 1,3;

结果如下：

SQL> set lines 1200;

SQL> select a.GROUP#,v$logfile b where a.GROUP#=

b.GROUP# order by 1,3;

GROUP# MEMBERS ARC STATUS MEMBER STATUS

---------- ---------- --- ---------------- ---------------------------------------- -------

1 2 NO CURRENT /u02/oracle/oradata/orcl/redo01.log

1 2 NO CURRENT /u01/redo/redo01_1.log

2 2 YES INACTIVE /u02/oracle/oradata/orcl/redo02.log

2 2 YES INACTIVE /u01/redo/redo02_1.log

3 2 YES INACTIVE /u02/oracle/oradata/orcl/redo03.log

3 2 YES INACTIVE /u01/redo/redo03_1.log

6 rows selected.

案例1：删除日志组成员中一个(不管是不是单前的还是非单前的redolog,下面方法都适用。)

rm -rf /u02/oracle/oradata/orcl/redo03.log

alter system switch logfile;

tail -f /u02/oracle/diag/rdbms/orcl/orcl/trace/alert_orcl.log

看到报错信息如下：

ORA-00313: open failed for members of log group 3 of thread 1

ORA-00312: online log 3 thread 1: '/u02/oracle/oradata/orcl/redo03.log'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

如何解决呢？先删除，在添加。

alter database drop logfile member '/u02/oracle/oradata/orcl/redo03.log';

alter database add logfile member '/u02/oracle/oradata/orcl/redo03.log' to group 3;

看log 没有报错：

Thread 1 advanced to log sequence 27 (LGWR switch)

Current log# 3 seq# 27 mem# 0: /u01/redo/redo03_1.log

Current log# 3 seq# 27 mem# 1: /u02/oracle/oradata/orcl/redo03.log

Thu Aug 31 19:28:50 2017

Archived Log entry 53 added for thread 1 sequence 26 ID 0x58497805 dest 1:

Archived Log entry 54 added for thread 1 sequence 26 ID 0x58497805 dest 2:

搞定。。。。。。

补充一下：

如果丢非当前的redolog 属于group 3,还可以这样解决：

alter database clear logfile group 3;

如果丢当前的redolog 属于group 3,还可以这样解决：

首先切换日志，让当前的redolog不属于group 3。

alter system switch logfile;

alter database checkpoint;

alter database clear logfile group 3;

案例2：如果redo日志没有多路复用，如果redo日志丢了，怎么办？

alter database drop logfile member '/u01/redo/redo01_1.log';

alter database drop logfile member '/u01/redo/redo02_1.log';

alter database drop logfile member '/u01/redo/redo03_1.log';

目前redo日志没有多路复用，信息如下：

select GROUP#,status from v$logfile order by 1;

GROUP# MEMBER STATUS

---------- -------------------------------------------------- -------

1 /u02/oracle/oradata/orcl/redo01.log

2 /u02/oracle/oradata/orcl/redo02.log

3 /u02/oracle/oradata/orcl/redo03.log

select a.GROUP#,3;

GROUP# MEMBERS ARC STATUS MEMBER STATUS

---------- ---------- --- ---------------- -------------------------------------------------- -------

1 1 YES ACTIVE /u02/oracle/oradata/orcl/redo01.log

2 1 NO CURRENT /u02/oracle/oradata/orcl/redo02.log

3 1 YES ACTIVE /u02/oracle/oradata/orcl/redo03.log

情况1：非当前redo日志丢失。

rm -rf /u02/oracle/oradata/orcl/redo03.log

模拟日志切换

alter system switch logfile;

报错信息：

ORA-00312: online log 3 thread 1: '/u02/oracle/oradata/orcl/redo03.log'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

执行命令：

alter database clear logfile group 3;

SQL> alter database clear logfile group 3;

alter database clear logfile group 3

ERROR at line 1:

ORA-00350: log 3 of instance orcl (thread 1) needs to be archived

ORA-00312: online log 3 thread 1: '/u02/oracle/oradata/orcl/redo03.log'

发现日志没有归档：

select a.GROUP#,3;

select name,NEXT_CHANGE# from v$archived_log;

SQL> select a.GROUP#,3;

GROUP# MEMBERS ARC STATUS MEMBER STATUS

---------- ---------- --- ---------------- -------------------------------------------------- -------

1 1 NO INACTIVE /u02/oracle/oradata/orcl/redo01.log

2 1 NO CURRENT /u02/oracle/oradata/orcl/redo02.log

3 1 NO INACTIVE /u02/oracle/oradata/orcl/redo03.log

执行命令：alter system checkpoint;

使用清空非归档的日志组命令：

alter database clear unarchived logfile group 3;

SQL> alter database clear unarchived logfile group 3;

Database altered.

在看看日志组3，结果有了：

[oracle@oracle250 ~]$ ll /u02/oracle/oradata/orcl/redo03.log

-rw-r----- 1 oracle dba 52429312 Aug 31 21:29 /u02/oracle/oradata/orcl/redo03.log

在看看信息如下：

SQL> select a.GROUP#,3;

GROUP# MEMBERS ARC STATUS MEMBER STATUS

---------- ---------- --- ---------------- -------------------------------------------------- -------

1 1 NO CURRENT /u02/oracle/oradata/orcl/redo01.log

2 1 YES ACTIVE /u02/oracle/oradata/orcl/redo02.log

3 1 YES ACTIVE /u02/oracle/oradata/orcl/redo03.log

搞定了。。。。。。。。。。。。。。。

注意一下：之前的备份失效了，重新进行热备份哦。(因为删除了redo03日志，导致redo03日志没有归档，导致归档scn不连续。因此需要重新备份。)

情况2：如果当前日志组丢了怎么办？

select a.GROUP#,3;

SQL> select a.GROUP#,3;

GROUP# MEMBERS ARC STATUS MEMBER STATUS

---------- ---------- --- ---------------- -------------------------------------------------- -------

1 1 NO CURRENT /u02/oracle/oradata/orcl/redo01.log

2 1 YES INACTIVE /u02/oracle/oradata/orcl/redo02.log

3 1 YES INACTIVE /u02/oracle/oradata/orcl/redo03.log

create table redo_01 as select * from scott.dept;

删除当前日志：

rm -rf /u02/oracle/oradata/orcl/redo01.log

SQL> startup;

ORACLE instance started.

Total System Global Area 2772574208 bytes

Fixed Size 2256472 bytes

Variable Size 771752360 bytes

Database Buffers 1979711488 bytes

Redo Buffers 18853888 bytes

Database mounted.

ORA-00313: open failed for members of log group 1 of thread 1

ORA-00312: online log 1 thread 1: '/u02/oracle/oradata/orcl/redo01.log'

ORA-27037: unable to obtain file status

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

数据库启动不了。具体信息上面。如何处理呢？

要利用热备份文件进行恢复，但是要丢失数据。。。。。

利用之前的备份文件还原回去。

之前的备份脚本如下：

[oracle@oracle250 ~]$ cat hotbackup.sh

sqlplus / as sysdba <<eof

!echo 'begin hot backup '

alter database begin backup;

!echo 'copy files'

!cp -v /u02/oracle/oradata/orcl/system01.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/sysaux01.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/undotbs01.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/users01.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/test01.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/rrr.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/tttt.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/tttt02.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/tttt03.dbf /home/oracle/hot_backup/

!cp -v /u02/oracle/oradata/orcl/temp01.dbf /home/oracle/hot_backup/

!echo 'end backup database'

alter database end backup;

exit

eof

还原数据。

cp /home/oracle/hot_backup/*.dbf /u02/oracle/oradata/orcl/

执行命令：

recover database until cancel;

SQL> recover database until cancel;

ORA-00279: change 1575684 generated at 08/31/2017 21:51:18 needed for thread 1

ORA-00289: suggestion : /u02/arch/1_34_953475378.dbf

ORA-00280: change 1575684 for thread 1 is in sequence #34

Specify log: {<RET>=suggested | filename | AUTO | CANCEL}

CANCEL

ORA-01547: warning: RECOVER succeeded but OPEN RESETLOGS would get error below

ORA-01195: online backup of file 1 needs more recovery to be consistent

ORA-01110: data file 1: '/u02/oracle/oradata/orcl/system01.dbf'

填写 AUTO | CANCEL都不行，怎么办呢？

SQL> alter database open resetlogs;

alter database open resetlogs

ERROR at line 1:

ORA-01195: online backup of file 1 needs more recovery to be consistent

ORA-01110: data file 1: '/u02/oracle/oradata/orcl/system01.dbf'

也不行。。。。。z在线求解答！！！！！！

(3)非归档模式丢失数据文件(不完全恢复---丢数据)

如果数据库处于noarchivelog模式下，如果丢失了任何数据文件，请执行如下任务：

1、如果实例没有关闭，请关闭实例

2、从备份还原整个数据库，包括所有数据文件、控制文件和重做redo文件。

3、打开数据库

4、让用户重新输入自上次备份以来所做的所有更改。

startup mount;

alter database noarchivelog;//改成非归档模式！！！！！！！

archive log list;

做一次冷备份。

select * from v$log;

select current_scn from v$database;

创建一张表，insert 一些数据。

影响：只能还原到备份之前的数据。备份之后的所有操作数据都丢了，好悲吹。这里我就不做实验了。

备注：数据库处于非归档状态，其联机日志循环覆盖使用，这意味着如果数据库需要进行介质恢复应用相关归档，

又由于非归档导致归档文件不存在，那么此时数据库只能执行基于取消的恢复，回退整个数据库到上一次全备份状态。

或者修改数据文件头部信息，来规避缺失归档。但不管怎么样都会丢失数据。

(4)归档模式丢失非关键数据文件

如果丢失某个数据文件，且该文件不属于system或undo表空间，则可以还原并恢复缺少的数据文件。。。。

已经打开归档模式：

SQL> archive log list

Database log mode Archive Mode

Automatic archival Enabled

Archive destination /u02/arch

Oldest online log sequence 47

Next log sequence to archive 49

Current log sequence 49

scott用户登录，创建一张表：

create table test as select * from dept;

select table_name,tablespace_name from dba_tables where table_name='TEST' and owner='SCOTT';

SQL> select table_name,tablespace_name from dba_tables where table_name='TEST' and owner='SCOTT';

TABLE_NAME TABLESPACE_NAME

------------------------------ ------------------------------

TEST USERS

查看表空间和文件名对应关系：

col file_name for a50

col tablespace_name for a10

col file_id for a50

select file_name,tablespace_name,file_id from dba_data_files where tablespace_name='USERS';

FILE_NAME TABLESPACE FILE_ID

-------------------------------------------------- ---------- ----------

/u02/oracle/oradata/orcl/users01.dbf USERS ##########

删除users表空间对应的数据文件。

rm -rf /u02/oracle/oradata/orcl/users01.dbf

SQL> select * from test;

select * from test

ERROR at line 1:

ORA-01116: error in opening database file 4

ORA-01110: data file 4: '/u02/oracle/oradata/orcl/users01.dbf'

ORA-27041: unable to open file

Linux-x86_64 Error: 2: No such file or directory

Additional information: 3

利用热备份的数据 cp