在启动数据库的时候,open阶段总是可能出现各种各样的问题，
比如让人胆战心惊的错误。
ORA-01113: file 1 needs media recovery

自己留意了一下，其实还是有蛮多的场景会出现这个问题，有些细节可能没有注意到就会出现这个问题，
比如我们重建控制文件的时候。
在重建控制文件之前做了shutdown abort的操作。

SQL> shutdown abort
ORACLE instance shut down.
SQL> startup nomount
ORACLE instance started.

Total System Global Area  314572800 bytes
Fixed Size                  1261564 bytes
Variable Size             163577860 bytes
Database Buffers          142606336 bytes
Redo Buffers                7127040 bytes
SQL> CREATE CONTROLFILE REUSE DATABASE "TEST10G" NORESETLOGS  NOARCHIVELOG
 .....
 26    '/u02/oracle/oradata/data02.dbf'
 27  CHARACTER SET US7ASCII
 28  ;

Control file created.
尝试启动数据库的时候就会抛出这个错误。

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/TEST10G/disk5/system01.dbf'

其实这个时候简单分析一下就会明白，上次是shutdown abort的方式，则对应的检查点信息无法写入数据文件，在open阶段smon会做这个校验。
开始在后台做数据的前滚，然后应用redo日志的数据，对某些操作做相应的回滚。
从下面的地方可以看出 last_change#没有任何值，表明上次断电重启后检查点信息没有写入。
SQL> select file#,checkpoint_change#,last_change# from v$datafile;

FILE# CHECKPOINT_CHANGE# LAST_CHANGE#
---------- ------------------ ------------
         1             858940
         2             858940
         3             858940
         4             858940
         5             858940

SQL> select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
         1             858940
         2             858940
         3             858940
         4             858940
         5             858940

SQL> select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            858939
这个时候尝试恢复数据库，再次观察，则相应的检查点信息就做了校正。

SQL> recover database;
Media recovery complete.
SQL>  select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            858939
SQL>  select file#,checkpoint_change#,last_change# from v$datafile;

FILE# CHECKPOINT_CHANGE# LAST_CHANGE#
---------- ------------------ ------------
         1             859017       859017
         2             859017       859017
         3             859017       859017
         4             859017       859017
         5             859017       859017

SQL> alter database open;

Database altered.
数据库启动之后，last_change#的值又回归零。等待稍后的检查点写入。

SQL>  select file#,checkpoint_change#,last_change# from v$datafile;

FILE# CHECKPOINT_CHANGE# LAST_CHANGE#
---------- ------------------ ------------
         1             879019
         2             879019
         3             879019
         4             879019
         5             879019

SQL>  select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            879019

其实这个过程中，恢复的基准就是检查点，也就是SCN.

当然在有些操作依赖于归档模式，介质恢复还是依赖于一些归档文件的。
像在非归档模式尝试下面的操作就不可行。

SQL> alter tablespace data offline immediate;
alter tablespace data offline immediate
*
ERROR at line 1:
ORA-01145: offline immediate disallowed unless media recovery enabled

SQL> alter tablespace data begin backup;
alter tablespace data begin backup
*
ERROR at line 1:
ORA-01123: cannot start online backup; media recovery not enabled

这个时候还是启用归档。

SQL> shut immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount
ORACLE instance started.

Total System Global Area  314572800 bytes
Fixed Size                  1261564 bytes
Variable Size             163577860 bytes
Database Buffers          142606336 bytes
Redo Buffers                7127040 bytes
Database mounted.
SQL> alter database archivelog ;

Database altered.

SQL> alter database open;

Database altered.
如果在归档模式中，使用热备份，需要声明begin backup,为了能够修复在热备份过程中可能产生的分裂数据块。

SQL> alter tablespace data begin backup;

Tablespace altered.
这个时候停库就会抛错。

SQL> shutdown immediate;
ORA-01149: cannot shutdown - file 5 has online backup set
ORA-01110: data file 5: '/u02/oracle/oradata/data02.dbf'
如果发生断电现象，则在重启的时候出现ORA-01113: file 5 needs media recovery就需要明辨这个错误背后的意思
SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area  314572800 bytes
Fixed Size                  1261564 bytes
Variable Size             163577860 bytes
Database Buffers          142606336 bytes
Redo Buffers                7127040 bytes
Database mounted.
ORA-01113: file 5 needs media recovery
ORA-01110: data file 5: '/u02/oracle/oradata/data02.dbf'

其实碰到这个错误，还是需要结合多种场景来考虑，比如查看是否热备份已经正常完成，之前的操作是什么样的？
SQL> desc v$backup
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 FILE#                                              NUMBER
 STATUS                                             VARCHAR2(18)
 CHANGE#                                            NUMBER
 TIME                                               DATE

SQL> select *from v$backup;

FILE# STATUS                CHANGE# TIME
---------- ------------------ ---------- ---------
         1 NOT ACTIVE                  0
         2 NOT ACTIVE                  0
         3 NOT ACTIVE                  0
         4 NOT ACTIVE                  0
         5 ACTIVE                 879352 20-JUL-15
可以从SCN的地方看出和重建控制文件的场景还是存在一定的差别。
SQL> select file#,checkpoint_change#,last_change# from v$datafile;

FILE# CHECKPOINT_CHANGE# LAST_CHANGE#
---------- ------------------ ------------
         1             879275
         2             879275
         3             879275
         4             879275
         5             879352

SQL> select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
         1             879275
         2             879275
         3             879275
         4             879275
         5             879352

SQL> select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            879275
明白了问题，修复就很容易了，果断结束热备份。

SQL> alter tablespace data end backup;

Tablespace altered.

SQL> select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
         1             879275
         2             879275
         3             879275
         4             879275
         5             879352

SQL> select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            879275
这个时候启动数据库就没有问题了。

SQL> alter database open;

Database altered.

SQL> select checkpoint_change# from v$database;

CHECKPOINT_CHANGE#
------------------
            899361

SQL>  select file#,checkpoint_change# from v$datafile_header;

FILE# CHECKPOINT_CHANGE#
---------- ------------------
         1             899361
         2             899361
         3             899361
         4             899361
         5             899361

其实热备份的这个错误也可以这么来处理。

SQL> alter tablespace data begin backup;

Tablespace altered.

SQL> shutdown abort
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area  314572800 bytes
Fixed Size                  1261564 bytes
Variable Size             163577860 bytes
Database Buffers          142606336 bytes
Redo Buffers                7127040 bytes
Database mounted.
ORA-01113: file 5 needs media recovery
ORA-01110: data file 5: '/u02/oracle/oradata/data02.dbf'

SQL> recover datafile 5;
Media recovery complete.
SQL> alter database open;

Database altered.

SQL> select *from v$backup;

FILE# STATUS                CHANGE# TIME
---------- ------------------ ---------- ---------
         1 NOT ACTIVE                  0
         2 NOT ACTIVE                  0
         3 NOT ACTIVE                  0
         4 NOT ACTIVE                  0
         5 NOT ACTIVE             899488 20-JUL-15

总之解决问题就行，SCN的部分着实是需要关注的一个重点，这也是备份恢复的基石。