052(四十一）

201.Why does performance degrade when many UPDATE, INSERT or DELETE statements are issued on a table that has an associated bitmap index?
A. The DML operations re-create the bitmap index blocks
B. The bitmap index is rebuilt automatically after a DML operation
C. The smallest amount of a bitmap that can be locked is a bitmap segment
D. Additional time is taken to remove NULL values from the bitmap index after a DML operation

Answer: AC

UNDO_TABLESPACE  Optional, and valid only in automatic undo management mode.

oracle数据库中一个实例只允许有一个活跃的还原表空间，且可以通过动态的方式切换还原表空间。

D：
是由DBCA自动创建或者由create database时手动创建或者create unod tablespace手动创建。
不是数据库启动时。