可以在最后一次增量后创建一个快照闪回点，如果失败，回退即可。查找失败原因再进行下一步。

alter database flashback on;
select flashback_on from v$database;
create restore point before_imp_tb guarantee flashback database;
select name from v$restore_point;

如果失败：
shutdown immediate
startup mount
falshback database to restore point before_imp_tb;