May 2020
Beginner to intermediate
319 pages
7h 3m
Chinese
Content preview from 数据库系统内幕
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共识
｜
269
为了证明这些状态是正确的，节点计算出到某个给定序列号为止的消息的状态。节点可
以比较摘要、验证状态的完整性，以及确保恢复过程中收到的消息加在一起达到的最终
状态是正确的。这一过程太昂贵，无法为每个请求执行。
每隔 N 个请求（N 是可配置的常量），主节点会创建一个
稳定检查点
（stable checkpoint）：
它广播一个最新序列号（标识执行结果已被反映在状态中的最后一个请求）以及相应状
态的摘要。然后，它等待 2f + 1 个副本响应，这些响应构成了该检查点的证明，保证
各副本可以安全地丢弃给定序列号之前的所有预准备、准备、提交和检查点消息。
理解拜占庭容错性很重要，它被用在有潜在对抗性的网络中的存储系统上。大多数时
候，对节点间通信进行身份验证和加密就足够了，但是当系统各部分之间没有信任时，
必须采用类似 PBFT 的算法。
容忍拜占庭故障的算法会带来显著的消息交换开销，因此，了解这些算法的使用场景格
外重要。文献 [BAUDET19] 和文献 [BUCHMAN18] 中还提到了一些其他协议，它们尝
试为包含大量参与者的系统优化 PBFT 算法。
14.6
本章小结
共识算法是分布式系统中最有趣的也是最复杂的主题之一。过去的几年中，涌现出了许
多新算法以及现有算法的多种实现，这证明了共识算法的重要性和流行程度日渐增长。
在本章中，我们讨论了经典 Paxos 算法以及 Paxos 的几个变体，每个变体都对不同的特
性进行了改进：
Multi-Paxos
允许提议者保留这一角色，提议多个值而不是一个。 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.