Recovering from the loss of an inactive redo log group.
从不活动的重做日志组的丢失中恢复。
Recovering from the loss of the current redo log group.
从当前重做日志组的丢失中恢复。
Recovering from the loss of an only active redo log group
从惟一活动重做日志组的丢失中恢复。
Recovering from the loss of one member of an online redo log group.
从丢失的联机重做日志组的成员中进行恢复。
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。
It is defined as "distance" between is and the end of the redo log.
它也被定义为从该位置到日志文件结束点的距离。
The redo log buffer is one-third full or contains 1 MB of buffered data.
在重做日志记录达到缓冲区的三分之一。
If the size of your redo log is 20m, you are taking 4 checkpoints for each log.
如果日志文件的大小为20m，你将在每个日志文件发生4次检查点。
It also contains the location in the redo log where the data block was last changed.
检查点队列中还包含日志文件中数据块最后一次被修改的位置。
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。
Normally, a switch occurs when the current online redo log file is full and writing must continue.
一般来说，当当前的在线重做日志文件已经满了并且还必须继续写的是偶，日志切换就会发生。
Maintaining multiple members of an online redo log group protects against the loss of the redo log.
保存在线重做日志文件组的多个成员来保证重做日志不丢失。
The position in the redo log where recovery is to start is referred to as the checkpoint position.
日志文件中数据库恢复开始的位置称作检查点位置。
Redo records can also be written to a redo log file before the corresponding transaction is committed.
基本意思如下对于重做记录，在相应的事务被提交之前，也能被写入重做日志文件。
This necessitates well-sized redo logs to avoid unnecessary checkpoints as a result of frequent log switches.
这个需求精心设计日志文件大小从而不会由于频繁的日志切换避免不必要的检查点。
Now that you are confirmed that the lost redo file is an ACTIVE redo log, shutdown the database - shutdown immediate.
既然您确认丢失的重做文件是active重做日志，那么现在就可以关闭数据库——shutdownimmediate。
Now that you are confirmed that the lost redo file is a CURRENT redo log, shutdown the database - shutdown immediate.
既然您确认丢失的重做文件是current重做日志，那么现在就可以关闭数据库——shutdownimmediate。
Now that you are confirmed that the lost redo file is an INACTIVE redo log, shutdown the database - shutdown immediate.
既然您已经确认丢失的重做文件是inactive重做日志，那么现在可以关闭数据库——shutdown immediate。
To investigate what status is the missing redo log is - Select * from v$logfile shows which group and member is INVALID
要检查丢失的重做日志处于什么状态 ——Select *fromv$logifle显示哪个组及哪个成员是无效的。
Checkpoint (CKPt) - Synchronizes the headers of data files and control files with the current redo log and checkpoint Numbers.
检查点(CKPt)——将数据文件头和控制文件头与当前重做日志和检查点数同步。
You can add or drop online redo log file groups or members to the primary database without affecting the standby database.
你可以在主库添加或删除在线重做日志组或者日志成员而不影响备库。
Ideally, the locations of the members should be on separate disks so that the failure of one disk does not cause the loss of the entire online redo log.
理论上说，日志文件组的成员的存放位置应该放在磁盘上的不同位置，这样即使一个磁盘损坏也不会导致整个在线重做日志文件丢失。
Redo Logfile Sizing Advisor - This feature recommends the optimal size of redo log files in order to avoid excessive disk I/Os due to frequent checkpointing.
Redo Logfile SizingAdvisor ——此特性推荐重做日志文件的最佳大小，从而避免因频繁出现的检查点而导致过多的磁盘I/O。
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。
Since the redo log group is inactive and is archived, just clear the redo log - alter database clear logfile group N (where N is the group # of the lost redo log)
由于重做日志组是不活动和归档的，所以只需清除重做日志即可 ——alterdatabaseclear logfilegroupN（其中 N 是丢失的重做日志的组 #）。
On the other hand, a larger number of changed objects per transaction means you lock changes for a longer time and your database also needs a bigger redo log.
另一方面，每次事务修改的对象数量越多就意味着锁定变更时间越长，同时数据库需要更大的redo log。
The maximum protection and maximum availability modes require that standby redo log files are configured on at least one standby database in the configuration.
最大保护和最大可用性模式需要备重做日志文件配置在配置中的至少一个备数据库上。
At some point, you need to resume redo apply on the standby database, and apply the archived redo log files to resynchronize the standby database with the primary database.
在有点伤，你需要在备库上重新应用重做数据，应用归档日志来同步备库和主库之间的数据。
When the CPU load goes up, the time taken for a log file sync round trip can increase even when the number of log file syncs and the volume of redo log generated doesn't change.
CPU负荷增长尽管(写)事务量没有变写日志个数没有变日志文件同步的往返信号传输时间就会延长。
Unless the redo log buffer is particularly full, only one synchronous writes is required per transaction. if piggybacking occurs, there can be less than one synchronous write per transaction.
除非重做日志缓冲区特别满，否则每个事务处理只需要一个同步写入。
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