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
｜
259
献 [LAMPSON01] 还区分了
外
Quorum 和
决策
Quorum，它们可转换为准备和接受阶段，
并给出了类似于柔性 Paxos 中的 Quorum 定义。
14.3.8
共识的推广解法
Paxos 解释起来可能不大容易：它包含多个角色和多个步骤，还有各式各样的变体，常
常令人难以跟上。但其实我们可以用更简单的方式思考它。之前我们将参与者分成各
种角色，还划分了决策回合，现在，我们可以只用一组简单的概念和规则来实现与单
回合 Paxos 相同的保证。我们对该方法仅做简短的讨论，因为这还是一个相对较新的
进展 [HOWARD19]
—
了解它很重要，虽然我们尚未看到它的实现和实际应用。
假设有一个客户端和一组服务器。每个服务器上有多个
寄存器
（register），每个寄存器用
一个下标来标识。寄存器只能被写入一次，它可能处于以下三种状态之一：未写入、包
含一个
值
或包含
nil
（一个特殊的空值）。
不同服务器中下标相同的寄存器构成一个
寄存器集
。每个寄存器集可以包含一个或多个
Quorum。根据其中的寄存器的状态，Quorum 可能处于
未决定
（Any 和 Maybe v）或
已
决定
（None 和 Decided v）两种状态之一：
Any
取决于将来的操作，该 Quorum 可以决定为任何值。
Maybe v
如果该 Quorum 做出一个决定，那个决定只能是 v。
None
该 Quorum 无法决定出值。
Decided v
该 Quorum 已经决定出值 v。
客户端与服务器交换消息并维护一个状态表，用于跟踪值和寄存器，并可以从中推断出 ...
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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.