Flashback日志管理的文档参考

Solution
Flashback logs are handled internally and we have no control over them. This means
that we cannot delete flashback logs manually, the ONLY way to delete then
is disabling FLASHBACK.

The FlashBack Logs can ONLY be deleted by DISABLING FLASHBACK
on database level

SQL> startup mount
     alter database flashback off;
     alter database open;

During space pressure, the Flashback logs are deleted under two
conditions:

1) When an archivelog is deleted, it would also delete the flashback logs
    that are dependent on the archived log.
2) When quota is shrunk, then flashback logs is deleted to reclaim disk
    space. This is decreasing the DB_RECOVERY_FILE_DEST_SIZE to such a value
     that the  FLB itself will run into a space pressure and than the old
     FLB\'s will get  deleted.

We can hit bellow bug and then the flashback logs are not deleted
even there is space pressure in the Flash backup disk space.