A. It saves disk space and reduces memory usage.
B. It saves disk space but has no effect on memory usage.
C. It incurs extra CPU overhead during DML as well as direct loading operations.
D. It incurs extra CPU overhead during DML but not direct loading operations.
E. It requires uncompress operation during I/O.
答案：（A、C）
解析：
《Administrator's guide》 20.2.6.3
随着数据库大小的增长,可以考虑使用表压缩.
压缩节省磁盘空间,减少database buffer cache中内存的使用,可以在读的过程中显著地加快查询的执行.
对于数据加载和DML操作,压缩在CPU开销上会有成本. 然而这种成本可以被减少的I/O需求抵销.