「TSDB」术语
RRD(Round Robin Database) RRD 数据库在创建的时候就已经定义好了大小，当存储空间满了之后，又从头开始覆盖旧的数据，适用于存储和时间序列相关的数据。RRD的大小可控，且不用维护。
A specialized storage system known as a Round Robin Database allows one to store large amounts of series information such as temperatures, network bandwidth, and stock prices with a constant disk footprint. It does this by taking advantage of changing needs for precision. As we will see later, the “round-robin " part comes from the basic data structure used to store data points: circular lists.
