79.You are working on a database that must be functioning 24 hours a day, 7 days a week. The databas
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79.You are working on a database that must be functioning 24 hours a day, 7 days a week. The database
is configured in ARCHIVELOG mode.
Which two options do you have for performing user-managed backups? (Choose two.)
A.You can perform consistent backups only.
B.You can perform a complete database backup without shutting down the database instance.
C.You can back up data files only when all data files have the same SCN recorded in the control file.
D.You can back up only those data files whose headers are frozen by using ALTER TABLESPACE BEGIN BACKUP or ALTER DATABASE BEGIN BACKUP commands.
答案:BD
解析:
A:错误,open状态下没有一致的备份
B:正确,由于是出于归档模式,因此备份不需要关闭数据库
C:错误,只有出于只读状态或者关闭的情况下,数据文件中的scn才会和控制文件中的scn一致的,这是因为increment checkpoint会修改控制文件中的scn,但是不修改
数据文件中的scn造成的
D:正确,ALTER TABLESPACE BEGIN BACKUP或者ALTER DATABASE BEGIN BACKUP--将表空间或者数据库置为备份状态
这个时候oracle会冻结对应的数据文件的头,执行完成后就可以复制物理文件进行备份了,备份完成后执行end backup命令
这个时候需要注意,在备份的时候虽然冻结了数据文件的头部,但是并不影响dml和select语句,这是由于虽然冻结了数据头文件,
但是这些操作都写到redo中了,select就更不会影响了,当end backup 后在dml修改的数据从buffer中写入数据文件中,
因此备份的时候需要
1.重做日志缓存区和重做日志文件适当的加大
2.在进行联机备份的时候每次只备份一个表空间
3.在dml操作最少的时间段来进行联机备份
is configured in ARCHIVELOG mode.
Which two options do you have for performing user-managed backups? (Choose two.)
A.You can perform consistent backups only.
B.You can perform a complete database backup without shutting down the database instance.
C.You can back up data files only when all data files have the same SCN recorded in the control file.
D.You can back up only those data files whose headers are frozen by using ALTER TABLESPACE BEGIN BACKUP or ALTER DATABASE BEGIN BACKUP commands.
答案:BD
解析:
A:错误,open状态下没有一致的备份
B:正确,由于是出于归档模式,因此备份不需要关闭数据库
C:错误,只有出于只读状态或者关闭的情况下,数据文件中的scn才会和控制文件中的scn一致的,这是因为increment checkpoint会修改控制文件中的scn,但是不修改
数据文件中的scn造成的
D:正确,ALTER TABLESPACE BEGIN BACKUP或者ALTER DATABASE BEGIN BACKUP--将表空间或者数据库置为备份状态
这个时候oracle会冻结对应的数据文件的头,执行完成后就可以复制物理文件进行备份了,备份完成后执行end backup命令
这个时候需要注意,在备份的时候虽然冻结了数据文件的头部,但是并不影响dml和select语句,这是由于虽然冻结了数据头文件,
但是这些操作都写到redo中了,select就更不会影响了,当end backup 后在dml修改的数据从buffer中写入数据文件中,
因此备份的时候需要
1.重做日志缓存区和重做日志文件适当的加大
2.在进行联机备份的时候每次只备份一个表空间
3.在dml操作最少的时间段来进行联机备份
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