Normally CR block buffer processing does not include the ‘gc cr block flush time’. However， when a CR buffer is cloned from a current buffer that has redo pending， a log flush for a CR block transfer is required. A high percentage is indicative of hot blocks with frequent read after write access.
有些时候，我们要清理数据库时，想把数据库中所有非系统自带的用户全部删除，在12C以前，我们只能通过人肉的方式，从12C 开始，多了一个字段： ORACLE_MAINTAINED如果时系统自带的，该值为Y,否则为N就很好办了，直接使用以下语句就可以找出系统自带的用户了。
