Datafile media recovery (often simply called media recovery) is the most basic form
of user-initiated data recovery. It can be used to recover from a lost or damaged
current datafile, SPFILE or control file. It can also recover changes that were recorded
in the redo logs but not in the datafiles for a tablespace that went offline without the
OFFLINE NORMAL option. Datafile media recovery can be performed whether you use
Recovery Manager or user-managed backup and recovery. (For user-managed backup
and recovery, it is in fact the main option available.)
数据文件介质还原（可以简单叫做介质还原）是最基本用户发起的数据还原。它可以从当前
丢失或者损坏文件中还原。SPFILE或者控制文件。它也可以还原那些已经记录在REDO日志
但没有写到数据文件对于一个表空间，它没有正常离线的改变。数据文件介绍还原可以被执行
不论你是用RMAN或者是用户管理的备份和还原。（对于用户管理的备份和还原。它其实是主要的
可用的选 项）
The need to restore a datafile from backup is not detected automatically. The first step
in performing media recovery is to manually restore the datafile by copying it from a
backup. Once a datafile has been restored from backup, however, the database does
automatically detect that this datafile is out of date and must undergo media recovery.
从备份中恢复的数据文件的需要并不是自动检测的。第一步执行介质还原是去通过从
备份中COPY文件去人工修复数据文件。一旦一个数据文件已经从备份中修复后，数据库
自动检测这个数据文件是否过时并且必须承受介质的还原。
Several situations force you to perform media recovery:
以下几种情况会迫使你去执行介质还原：
■ You restore a backup of a datafile.
■ You restore a backup control file (even if all datafiles are current).
■ A datafile is taken offline (either by you or automatically by the database) without
the OFFLINE NORMAL option.
#修复备份的数据文件
#修复备份的控制文件
#一个数据文件离线（或者是你或者是数据库自动）在没有正常的OFFLINE选项时。
For a datafile to be available for media recovery, one of two things must be true:
对于一个数据文件从介质还原中变得可用，以下2者之一必须为真：
■ The database that the datafile belongs to must not be open;
or
■ The specific datafile needing recovery must be offline, if the database is open.
#属于数据库中的文件必须是打开的
或者
#指定需要还原的数据文件必须离线。如果数据库是打开的。
A datafile that needs media recovery cannot be brought online until media recovery
has been completed. A database cannot be opened if any of the online datafiles needs
media recovery.
一个需要还原的数据文件不能联机的直接介质还原已经成功。一个数据库不能打开的如果
如果联机的数据文件有需要介质还原。
You can manage the expected duration of media recovery as part of your backup and
recovery strategy. It is affected by, for example, the frequency of backups and parallel
recovery parameters.
你可以管理介质还原的时期作为你备份和还原的策略。它受到一些因素影响，如频繁的备份
和并行的还原参数。
