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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4
｜
第
1
章
向扩展通常是阻力最小的途径，但它也有缺点：大型机器一般非常昂贵，而且在最终达到
物理极限时，就无法再升级到更高的配置了。另一种方式是横向扩展：如果想增加存储空
间或增加读写操作的吞吐量，那么可以购买额外的服务器，并将它们添加到集群中。这既
便宜又便于扩展，但管理
1000
台机器比管理
1
台机器困难得多。
MongoDB
的设计采用了横向扩展
。面向文档的数据模型使跨多台服务器拆分数据更加容
易。
MongoDB
会自动平衡跨集群的数据和负载
，自动重新分配文档，并将读写操作路由
到正确的机器上，如图
1-1
所示。
应用程序
驱动程序
应用程序
驱动程序
mongos
（路由节点）
应用程序
分片节点 分片节点
数据 数据
驱动程序
配置服务器
配置服务器
配置服务器
图 1-1：使用分片将 MongoDB 横向扩展至多台服务器
MongoDB
集群的拓扑结构，或者说其连接的是一个集群还是单个节点，对应用程序来说
都是透明的。这使得开发人员能够专注于应用程序的开发，而无须考虑扩展问题。同样，
如果需要扩展现有部署的拓扑结构以支持更多负载，那么也无须更改应用程序的逻辑。
1.3
功能丰富
MongoDB
是通用型数据库，除了创建、读取、更新和删除数据外，它还提供了数据库管
理系统的常见功能和许多其他独特的功能，举例如下。
索引
MongoDB
支持通用的二级索引
，并提供唯一索引、复合索引、地理空间索引及全文索
引功能。此外，它还支持在不同层次结构（如嵌套文档和数组）上建立二级索引，让开
发人员能够以最适合应用程序的方式充分利用其建模能力。
聚合
MongoDB ...
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