基本概念：
1> Read amplification is the number of I/O’s required to satisfy a particular query.
读放大：一次指定查询所需的IO操作数目。
2> Write amplification is the amount of data written to storage compared to the amount of data that the application wrote.
写放大：实际写入磁盘的数据大小比上用户期望程序写入的数据量。
3> Space amplification is the space required by a data structure can be inflated by fragmentation or requirements for temporary copies of the data.
空间放大：存储采用的数据结构因分裂或临时数据拷贝造成的磁盘空间占用放大。
