November 2021
Intermediate to advanced
410 pages
12h 1m
Chinese
Content preview from MongoDB权威指南（第3版）
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332
第 20章
持久性
持久性是数据库系统的一种属性，它保证了提交给数据库的写操作将永久保存在数据库
中。如果票务预订系统通知你音乐会座位已经成功预订，那么即使预订系统的某些程序崩
溃，你的座位也是被成功预订的。对于
MongoDB
来说
，需要考虑的是集群（或者更具体
地说就是副本集）级别的持久性。
本章内容包括：
• MongoDB
如何通过日志机制保证副本集成员级别的持久性；
• MongoDB
如何使用写关注保证集群级别的持久性；
•
如何配置应用程序和
MongoDB
集群，以提供所需要的持久性级别；
• MongoDB
如何使用读关注保证集群级别的持久性；
•
如何在副本集中设置事务的持久性级别。
本章讨论的是副本集的耐久性。一个三成员副本集是生产环境推荐的最基本集群。这里的
讨论适用于拥有更多成员的副本集和分片集群。
20.1
使用日志机制的成员级别持久性
为了在服务器发生故障时提供持久性，
MongoDB
使用了一种称为
日志
（
journal
）的预写
式日志（
WA
L
）机制。
WAL
是数据库系统中一种常用的持久性技术，其基本原理是，在
将对数据库所做的更改应用到数据库本身之前，将对这些更改的一种表示写到持久介质
（如磁盘）上。在许多数据库系统中，
WA
L
也被用来提供原子性这一数据库属性。然而，
MongoDB
使用其他技术来确保原子写入。
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