May 2020
Beginner to intermediate
319 pages
7h 3m
Chinese
Content preview from 数据库系统内幕
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266
｜
第
14
章
它的承诺
—
成为一个可靠的一致性算法。
14.5
拜占庭共识
到目前为止，我们讨论的所有共识算法都假定不存在拜占庭故障（参见 8.7.3 节）。换句
话说，节点都“诚实”地执行算法，而不是尝试利用算法或伪造结果。
我们将看到，这一假设允许以更少的可用参与者达成共识，并且一次提交所需的网络交
互次数更少。但是，有时分布式系统也会部署在有潜在对抗性的环境中，其中各节点并
非由同一实体控制，我们需要用算法来保证：即使在某些节点行为失常甚至带有恶意的
情况下，系统仍然能够正常运行。除了人为的恶意之外，拜占庭式故障还可能由 bug、
错误配置、硬件问题或数据损坏引起。
大多数拜占庭共识算法需要用 N
2
条消息完成一个算法步骤，其中 N 表示 Quorum 的大
小，因为 Quorum 中的每个节点都必须与其他所有节点通信。每个步骤都需要用其他节
点做交叉验证，这么做是必需的，因为节点不能彼此信赖，也不能依赖领导者，必须将
返回的结果与多数响应进行比较才能验证其他节点的行为。
我们在这里只讨论一种拜占庭共识算法：实用拜占庭容错（Practical Byzantine Fault
Tolerance, PBFT）[CASTRO99]。PBFT 假定节点故障相互独立（即，故障可能会相互配
合，但不能立即或至少不会以相同的方式接管整个系统）。系统具有弱同步假设，就像
你期望中的正常网络那样：故障可能会发生，但不会无限持续下去，最终一定会恢复。
节点间的所有通信都经过加密，以防止伪造消息或网络攻击。副本知道彼此的公钥 ...
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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.