Creates the online redo log files if they do not currently exist.

联机日志损坏，不能做完整修复时，用的。

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Changing the size and number of the online redo log files is sometimes done to tune the database.

改变在线重做日志文件大小和数量有时是优化数据库。

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Whenever you add an online redo log file to the primary database, you should add corresponding online and standby redo log files to the standby database.

无论何时，你在主库添加在线重做日志文件，你应该在备库添加相应的在线重做日志和备用重做日志文件。

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