-----buffer 与cache 的区别
A buffer is something that has yet to be "written" to disk.
A cache is something that has been "read" from the disk and stored for later use.
BUFFER的使用是为了缓解IO的差异,是解决速度差异,提高传输效率,保证异步读写的有利工具
CACHE是为了避免频繁的LOAD/UNLOAD.CACHE有很多算法,保证如何把最常用的数据放在里面,提高系统的性能