OCP-1Z0-053-V13.02-95题

jxp2002

　　
　　95.Examine the following scenario: The target database instance is running. The most recent backup
　　available for the target database was taken two days ago. Log files switches have occurred in last two
　　days. The target database is duplicated on the same host, using the Recovery Manager (RMAN)
　　duplicate command as follows:
　　RMAN> RUN { ALLOCATE AUXILIARY CHANNEL aux 1 DEVICE TYPE DISK;
　　DUPLICATE TARGET DATABASE TO auxdb; }
　　Which statement is true about the duplicate database in this scenario?
　　A. It contains data till the last backup
　　B. It contains all data from target database until the current time
　　C. It contains all data from only the committed transactions in the target database
　　D. It contains all data except that which is used by the transactions in the current online redo file of target database
　　Answer: D
　　答案解析：
　　官方参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmdupdb.htm#BRADV423
　　从命令可看出，是使用AUXILIARY CHANNEL基于 backup-based的复制数据库。
　　

　　RMAN must perform database point-in-time recovery, even when no explicit point in time is provided for duplication. Point-in-timerecovery is required because the online redo log files in the source database are not backed up and cannot be applied to the duplicate database. The farthest point of recovery of the duplicate database is the most recent redo log file archived by the sourcedatabase.
　　

　　从这句话可以看出，复制数据库是基于时间点的恢复，意味着在source database的在线重做日志没有被备份，所以不能被应用到duplicate database，故最多能恢复到source database最近的归档重做日志所包含的数据，即在target database即source database中正在记录事务的重做日志不能包含到duplicate database里去。
　　故选D
　　
How RMAN Duplicates a Database
For backup-based duplication, the principal work of the duplication is performed by the auxiliarychannels. These channels correspond to a server session on the auxiliary instance on the destination host. For active database duplication the primary work is performed by target channels.
　　RMAN must perform database point-in-time recovery, even when no explicit point in time is provided for duplication. Point-in-timerecovery is required because the online redo log files in the source database are not backed up and cannot be applied to the duplicate database. The farthest point of recovery of the duplicate database is the most recent redo log file archived by the sourcedatabase.
As part of the duplicating operation, RMAN automates the following steps:

• 　　Creates a default server parameter file for the auxiliary instance if the following conditions are true:
  
  
  
  • 　　Duplication does not involve a standby database.
    
  • 　　Server parameter files are not being duplicated.
    
  • 　　The auxiliary instance was not started with a server parameter file.
    
  
  
• 　　Restores from backup or copies from active database the latest control file that satisfies the UNTIL clause requirements.
  
• 　　Mounts the restored or copied backup control file from the active database.
  
• 　　Uses the RMAN repository to select the backups for restoring the data files to the auxiliary instance. This step applies to backup-based duplication.
  
• 　　Restores and copies the duplicate data files and recovers them with incremental backups and archived redo log files to a noncurrent point in time.
  
• 　　Shuts down and restarts the database instance in NOMOUNT mode.
  
• 　　Creates a new control file, which then creates and stores the new DBID in the data files.
  
• 　　Opens the duplicate database with the RESETLOGS option and creates the online redo log for the new database.
  

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