Datafile media recovery(often simply called media recovery) is the most basic form of user-initiated data recovery.
Crash recovery process is a special form of recovery,witch happens the first time an Oracle database instance is started after a crash (or SHUTDOWN ABORT).In Crash recovery,the goal is to bring the datafiles to a transaction-consistent state,preserving all committed changes up to the point when the instance failed.
两者的重要区别：
1、Media recovery must be explicitly invoked by a user.The database will not run media recovery on its own.
2、Media recovery applies needed changes to datafiles that have been restored from backup,not to online datafiles left over after a crash.
3、Media recovery must use archived logs as well as the online logs, to find changes reaching back to the time of the datafile backup.
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