闪回数据库
闪回数据库
在物理级别上，Oracle 闪回数据库提供了一个比database point-in-time recovery(DBPITR)更有效的数据保护。如果当前数据文件发生了些我们不想要的改变，可以用RMAN的FLASHBACK DATABASE命令来把数据库文件的内容恢复到某个时间之前。这个和DBPITR有些像，但是总的来说要比它快，因为闪回不需要从备份中恢复数据文件，而且不需要用太多的redo来进行介质恢复。
闪回数据库通过闪回日志来得到数据块的之前版本，也是通过这个来得到归档重做日志的信息。闪数据库需要你为数据库配置一个叫做flash recovery area的路径，来放闪回日志，因为闪回日志只能放到这里面。闪回在默认条件下是不启用的。用于存放闪回日志的存储空间由数据库自动分配与放在flash recovery area的路径的其它文件达到平衡。
oracle数据库也支持恢复点，可以与闪回数据库，备份，恢复配合使用。恢复点其实就是system change number(SCN)的别名。你可以在任何时间创建一个恢复点，并且把数据库中的内容部分或者全部恢复到该时间点。一个靠得住的恢复点可以保证你用闪回数据库的方法把数据库恢复到恢复点的状态。
At the physical level, Oracle Flashback Database provides a more efficient data
protection alternative to database point-in-time recovery (DBPITR). If the current
datafiles have unwanted changes, then you can use the RMAN command FLASHBACK
DATABASE to revert the datafiles to their contents at a past time. The end product is
much like the result of a DBPITR, but is generally much faster because it does not
require restoring datafiles from backup and requires less redo than media recovery.
Flashback Database uses flashback logs to access past versions of data blocks and
some information from archived redo logs. Flashback Database requires that you
configure a flash recovery area for a database because the flashback logs can only be
stored there. Flashback logging is not enabled by default. Space used for flashback logs
is managed automatically by the database and balanced against space required for
other files in the flash recovery area.
Oracle Database also supports restore points in conjunction with Flashback Database
and backup and recovery. A restore point is an alias corresponding to a system
change number (SCN). You can create a restore point at any time if you anticipate
needing to return part or all of a database to its contents at that time. A guaranteed
restore point ensures that you can use Flashback Database to return a database to the
time of the restore point.