Which statements are true regarding table compression? (Choose all that apply.)
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.
A and C are correct:
https://docs.oracle.com/cd/B28359_01/server.111/b28310/tables002.htm
Consider Using Table Compression
As your database grows in size to gigabytes or terabytes and beyond, consider using table compression. Table compression saves disk space and reduces memory use in the buffer cache. Table compression can also speed up query execution during reads. There is, however, a cost in CPU overhead for data loading and DML. Table compression is completely transparent to applications. It is especially useful in online analytical processing (OLAP) systems, where there are lengthy read-only operations, but can also be used in online transaction processing (OLTP) systems.