Oracle online recovery depends a great deal on what is actually lost , for example , losing a group on online redo logs , losing a rollback segment data file , or corrumption of a data file for the system table space Oracle联机恢复很大程度上取决于实际丢失了什么，例如，在联机重做日志上丢失了一个组、丢失了回滚段数据文件或者system表空间的数据文件的损坏。
For a long running transaction when all logs are active , online redo logs will only be overwritten if either you manually archive the non - active online redo or that you have the arch process to do it for you 对于长期运行的事务，当所有日志都处于活动状态时，如果手动对非活动联机重做进行归档，或者让arch进程来为您完成这项工作，那么只需重写联机重做日志即可。
The entire notion of online backup in oracle is that as users carry out transactions , all changes made to the database , either committed or uncommitted , are stored to the redo log buffer and subsequently are written to the online redo log files by the lgwr process 在oracle中，联机备份的全部思想是，当用户执行事务时，将对数据库所做的所有更改（提交或未提交的）都存储到重做日志缓冲区中，随后由lgwr进程把它们写到联机重做日志文件中。
