About Logging for Flashback Database and Guaranteed Restore Points【每日一译】--20121120

The logging for Flashback Database and guaranteed restore points is based upon

capturing images of datafile blocks before changes are applied, so that these images

can be used to return the datafiles to their previous state when a FLASHBACK

DATABASE command is executed.

对于闪回数据库的日志和保证修复点是基于捕获的数据块镜像在改变之前，所以这些镜像

可以将数据文件返回到先前的状态，当FLASHBACK DATABASE命令执行时。

The chief differences between normal flashback logging and logging for guaranteed

restore points are related to when blocks are logged and whether the logs can be

deleted in response to space pressure in the flash recovery area. These differences

affect space usage for logs and database performance.

对于正常的闪回日志和对于保证点的日志的最大不同点都是关于什么时候块产生日志？日志

是否能被删除对于在闪回区中的空间压力。这些不同影响空间的使用对于日志和数据库性能。

Whether to enable logging for flashback database, use guaranteed restore points, or

both depends upon your recoverability goals, and the implications in performance and

in space usage for these features, separately and when used together.

对于FLASH DATABASE是否允许日志，使用保证修复点，或者两者依赖于你可还原的目标，

并且对于这些功能在性能和空间使用上的影响，单独和一起使用的功能影响。

Guaranteed Restore Points and Flash Recovery Area Space Usage

When you create a guaranteed restore point, with or without enabling full flashback

database logging, you must monitor the space available in your flash recovery area.

No file in the flash recovery area is eligible for deletion if it is required to satisfy the

guarantee. Thus, retention of flashback logs and other files required to satisfy the

guarantee, as well as files required to satisfy your backup retention policy, can cause

the flash recovery area to fill completely.

保证修复点和闪回区域空间使用

当你创建一个保证修复点时，有或者没有允许全部闪回数据库日志，你必须监控在闪回区中的

可用空间。在闪回区是没有文件符合删除的，如果它要求满足保证修复点情况。那样话，闪回

日志的期限和其它文件被要求去满足保证点，为了满足你备份期限的策略的文件可以会导致闪回

区被完全的充满。

Caution: If no files are eligible for deletion from the flash recovery

area because of the requirements imposed by your retention policy

and the guaranteed restore point, then the database behaves as if it

has encountered a disk full condition. In many circumstances, this

causes your database to halt. See "When Space is Not Available in the

Flash Recovery Area" on page 3-21 for more information on the effects

of a full flash recovery area.

警告：如果闪回区没有文件符合删除因为要求被期限策略和保证修复点规定，

那么数据库工作如果它遭遇磁盘满的情况。在很多情况下，这将导致你的数据库

挂起。