11g閃回日誌(flashback log)保留時間引數 - db_flashback_retention_target

檢視  DB_FLASHBACK_RETENTION_TARGET 引數是預設值 1440 (分鐘)， 即一天時間。 文件對於它的解釋如下：

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.    

但是實際測試中發現， 只要 flashback 區足夠大，歸檔檔案不刪除，系統都可以回退到超過1天的某個歷史時間點， 沒有對閃回日誌
檔案進行覆蓋 。 

版主 ： 我覺得這個和control_file_record_keep_time樣，只是代表了一天前的flashback log可以被刪除，但是否刪除，還是看fra使用率是否達到那個閾值。

作者的話： 這裡的閥值應該指的是 引數 db_recovery_file_dest_size 設定的大小 ，這個大小隻是一個閥值，不會佔用空間。

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.

詳情參考 ：  http://www.itpub.net/thread-1864839-1-1.html