Key compression can lead to a huge saving in space, letting you store more keys in
each index block, which can lead to less I/O and better performance.

Although key compression reduces the storage requirements of an index, it can
increase the CPU time required to reconstruct the key column values during an index
scan. It also incurs some additional storage overhead, because every prefix entry has
an overhead of 4 bytes associated with it.

性能以及存储上的考虑
1. 可以在索引块中存储跟过的索引键 ，减少I/O ，提高性能 ，节省空间
2. 当执行索引扫描时 ，要重构键值 ，因此增加了 CPU 的负担
3. 键压缩也会导致额外的存储开销 ，因为每个前缀需要4字节的管理开销