1、rrdtool简介

这是官方文档的原话：

RRDtool refers to Round Robin Database tool.

Round robin is a technique that works with afixed amount of data, and a pointer to the current element.

Think of a circle with some dots plotted on the edge. These dots are the places where data can be stored.

Draw an arrow from the center of the circle to one of the dots; this is the pointer.

When the current data is read or written, the pointer moves to the next element.

As we are on a circle there isneither a beginning nor an end, you can go on and on and on.

After a while, all the available places will be used and the processautomatically reuses old locations.

This way, the dataset will not grow in size and thereforerequires no maintenance.

RRDtool works with Round Robin Databases (RRDs). It stores and retrieves data from them.

rrd 的 key words：

环形，固定大小，自动维护

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不得不提一个名词，时序数据库。

推荐阅读下面三篇 references：

1、http://www.infoq.com/cn/articles/database-timestamp-01

2、http://www.infoq.com/cn/articles/database-timestamp-02

3、http://www.infoq.com/cn/articles/database-timestamp-03