修改数据库archivelog模式

2014年2月14日
今天遇到执行alter tablespace example begin backup 时报错，ora-01123: cannot start online

backup:media recovery not enabled，首先想到数据库是处在noarchivelog 模式。
如何修改呢？
解决方法：
SQL> shutdown immediate
Database closed.
Database dismounted.

SQL> startup mount
ORACLE instance started.
Total System Global Area  285212672 bytes
Fixed Size                  1218992 bytes
Variable Size             104859216 bytes
Database Buffers          176160768 bytes
Redo Buffers                2973696 bytes
Database mounted.

SQL> alter database archivelog;
Database altered.

SQL> alter database open;
Database altered.

SQL> archive log list
database log mode              Archive Mode
Automatic archival             Enabled
Archive destination            USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence     1
Next log sequence to archive   3
Current log sequence           3

SQL> alter tablespace example begin backup;

问题解决