分布式一致性算法Paxos介绍
https://segmentfault.com/a/1190000005717258
Paxos协议超级详细解释+简单实例
http://blog.csdn.net/cnh294141800/article/details/53768464
undo和redo的区别
http://meng702.iteye.com/blog/1008638
http://liwenshui322.iteye.com/blog/1488949
http://blog.163.com/jing_playboy/blog/static/757362222012520104521864/