11g R2中 DB_FLASHBACK_RETENTION_TARGET 如何理解

tolywang

Oracle 11.2.0.3  

查看  DB_FLASHBACK_RETENTION_TARGET 参数是默认值 1440 (分钟)， 即一天时间。 文档对于它的解释如下：

DB_FLASHBACK_RETENTION_TARGET specifies the upper limit (in minutes) on how far back in time the database may be flashed back. How far back one can flashback a database depends on how much flashback data Oracle has kept in the flash recovery area.     

但是实际测试中发现， 只要 flashback 区足够大，归档文件不删除，系统都可以回退到超过1天的某个历史时间点， 没有对闪回日志
文件进行覆盖 。 这个参数具体如何理解  ？  

zergduan

我觉得这个和control_file_record_keep_time样，只是代表了一天前的flashback log可以被删除，但是否删除，还是看fra使用率是否达到那个阈值

Yong Huang

I searched on MOS but couldn't find an answer. Zergduan's explanation may be right.

I remember we used to enable flashback database on our 10gR2 database. It quickly ran out of space and, contrary to what we learned, the logs were not automatically deleted. I don't think we set any guaranteed restore point, and the DB_FLASHBACK_RETENTION_TARGET setting was not outrageous. We stopped doing it anyway.