11g闪回日志(flashback log)保留时间参数 - db_flashback_retention_target
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 。
版主 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。
作者的话： 这里的阀值应该指的是 参数 db_recovery_file_dest_size 设置的大小 ，这个大小只是一个阀值，不会占用空间。
版主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.
详情参考 ： http://www.itpub.net/thread-1864839-1-1.html
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 。
版主 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。
作者的话： 这里的阀值应该指的是 参数 db_recovery_file_dest_size 设置的大小 ，这个大小只是一个阀值，不会占用空间。
版主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.
详情参考 ： http://www.itpub.net/thread-1864839-1-1.html
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