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2997ms reviewed Jun 20, 2020
| 现在我们将继续沿着同样的路线前进，寻求可以让应用忽略分布式系统部分问题的抽象概念。例如，分布式系统最重要的抽象之一就是**共识（consensus）**：**就是让所有的节点对某件事达成一致**。正如我们在本章中将会看到的那样，尽管存在网络故障和流程故障，可靠地达成共识是一个令人惊讶的棘手问题。 | ||
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| 一旦达成共识，应用可以将其用于各种目的。例如，假设你有一个单主复制的数据库。如果领导者挂掉，并且需要故障切换到另一个节点，剩余的数据库节点可以使用共识来选举新的领导者。正如在“[处理节点宕机](ch5.md#处理节点宕机)”中所讨论的那样，重要的是只有一个领导者，且所有的节点都认同其领导。如果两个节点都认为自己是领导者，这种情况被称为**脑裂（split brain）**，且经常导致数据丢失。正确实现共识有助于避免这种问题。 | ||
| 一旦达成共识，应用可以将其用于各种目的。例如，假设你有一个单主复制的数据库。如果主库挂掉，并且需要故障切换到另一个节点，剩余的数据库节点可以使用共识来选举新的领导者。正如在“[处理节点宕机](ch5.md#处理节点宕机)”中所讨论的那样，重要的是只有一个领导者，且所有的节点都认同其领导。如果两个节点都认为自己是领导者，这种情况被称为**脑裂（split brain）**，且经常导致数据丢失。正确实现共识有助于避免这种问题。 |
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这里如果改成主库的话，后面的“领导者”是不是都应该改成“主库”？
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https://github.com/Vonng/ddia/blob/master/ch5.md#%E9%A2%86%E5%AF%BC%E8%80%85%E4%B8%8E%E8%BF%BD%E9%9A%8F%E8%80%85
而且我觉得这里“领导者” 和 “主库”的意思是一样的，好像没必要改。
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我已经不记得当时为啥提这个PR了…可能是单纯觉得“单主复制”和“领导者”不太匹配？
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| 原来“硬核空间”的大牛也在看ddia啊，居然在这里碰到了。。。 |
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