1：redo log 是如何工作的： Online redo logs store a record of transactions that have occurred in your database. Online r
1：redo log 是如何工作的：
Online redo logs store a record of transactions that have occurred in your database. Online redo logs exist solely to provide a mechanism for you to recover your database in the event of a failure. You are required to have at least two online redo log groups in your database. Each online redo log group must contain at least one online redo log member. The member is the physical file that exists on disk. You can create multiple members in each redo log group, which is known as multiplexing your online redo log group.
NOTE：联机重做日志记录数据库发生的所有变化。联机重做日志采用循环些的处理方法
2：如何尽量减少redo错误造成的数据损失：
•Multiplex groups to have multiple members.
•Never allow two members of the same group to share the same controller.
•Never put two members of the same group on the same physical disk.
•Ensure operating system file permissions are set appropriately.
•Use physical storage devices that are redundant (that is, RAID).
•Appropriately size the log files so that they switch and are archived at regular intervals.
•Set the archive_lag_targetinitialization parameter to ensure that the online redo logs
are switched at regular intervals
3：Determining How to Restore
select a.group#,a.thread# ,a.status ,b.member member,b.status from v$log a,v$logfile b where a.group#=b.group# order by a.group#,b.group#；
