May 2020
Beginner to intermediate
319 pages
7h 3m
Chinese
Content preview from 数据库系统内幕
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领导者选举
｜
181
图 10-1 展示了霸道领导者选举算法：
•
a) 进程 3 注意到前一个领导者 6 已崩溃，于是向具有更高标识符的进程发送选举消
息来开始新的选举。
•
b) 4 和 5 回应 Alive（存活）消息，因为它们具有比 3 更高的排名。
•
c) 3 通知在此轮响应中排名最高的进程 5。
•
d) 5 被选为新的领导者，它广播 Elected（选举完成）消息，将选举结果通知排名
较低的进程。
a） b） c） d）
图
10-1
：霸道算法。以前的领导者（
6
）发生故障，进程
3
发起新的选举
这种算法的一个明显问题是，在存在网络分区的情况下，它违反了安全性保证（一次最
多只能选举一个领导者）。很容易出现这样的情况：节点将被分成两个或多个独立运行
的子集，每个子集选举出了这个子集的领导者。这种情况被称为
脑裂
（split brain）。
该算法的另一个问题是对排名较高节点有强烈的偏向性，如果这些节点不稳定，可能导
致算法一直处于重新选举状态。一个不稳定的高排名节点提议出任领导者，此后不久发
生故障，稍后又再次赢得选举，然后再次发生故障，整个过程重复进行。可以通过分发
主机质量的度量并在选举时将其纳入考虑因素来解决这一问题。
10.2
依次故障转移
霸道算法有许多改进其各种性质的版本。例如，我们可以使用多个依次（next-in-line）
替代进程作为故障转移候选来缩短重选过程 [GHOLIPOUR09]。
每个选举出的领导者都提供一个故障转移节点的列表。当其中一个进程检测到领导者故
障时，它通过向列表中排名最高的 ...
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