77. You executed the following command to perform a backup of the USERS tablespace:
SQL> ALTER TABLESPACE users BEGIN BACKUP;
ALTER TABLESPACE users BEGIN BACKUP
*
ERROR at line 1:
ORA-01123: cannot start online backup; media recovery not enabled
What could be the reason for this error?
A.The MTTR Advisor is disabled.
B.The database is in NOARCHIVELOG mode.
C.The tablespace is already in backup mode.
D.The Flash Recovery Area is not configured.
Answer: B
对数据库进行热备，必须把数据库设置为archivelog 模式。
如果未处于archivelog 模式，需shutdown数据库，启动到mount状态进行修改。因此B是正确答案。
1、现象重现：
sys@TEST0910> alter tablespace users begin backup;
alter tablespace users begin backup
*
ERROR at line 1:
ORA-01123: cannot start online backup; media recovery not enabled
2、查看归档模式：
sys@TEST0910> archive log list;
Database log mode No Archive Mode
Automatic archival Disabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 28
Current log sequence 30
3、在mount模式下进行归档模式修改。
sys@TEST0910> shutdown immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
sys@TEST0910> startup mount;
ORACLE instance started.
Total System Global Area 2505338880 bytes
Fixed Size 2230952 bytes
Variable Size 587203928 bytes
Database Buffers 1895825408 bytes
Redo Buffers 20078592 bytes
Database mounted.
sys@TEST0910> alter database archivelog;
Database altered.
4、查看修改结果，已经为归档模式
sys@TEST0910> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 28
Next log sequence to archive 30
Current log sequence 30
5、开启数据库，进行联机备份
sys@TEST0910> alter database open;
Database altered.
sys@TEST0910> alter tablespace users begin backup;
Tablespace altered.
操作系统命令拷贝users.dbf文件；
sys@TEST0910> alter tablespace users end backup;
Tablespace altered.