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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MongoDB
简介
｜
5
特殊的集合和索引类型
MongoDB
支持生命周期有限
（
TTL
）集合，适用于保存将在特定时间过期的数据，比
如会话和固定大小的集合，以及用于保存最近的数据（日志）。
MongoDB
还
支持部分索
引，可以仅对符合某个条件的文档创建索引，以提高效率并减少所需的存储空间。
文件存储
针对大文件及文件元数据的存储，
MongoDB
使用了一种非常易用的协议。
MongoDB
并不具备关系数据库中的一些常见功能
，特别是复杂的连接操作。
MongoDB
通
过使用
3.2
版本引入的
$lookup
聚合运算符以非常有限的方式支持连接操作。在
3.6
版本
中，可以使用多个连接条件以及非关联子查询来实现更复杂的连接。
MongoDB
的这种处
理是出于架构上的考虑，以便获得更好的可扩展性，因为这些特性在分布式系统中很难高
效地实现。
1.4
性能卓越
性能是
MongoDB
的重中之重，这一点决定了它的许多设计。它在其
WiredTiger
存储引擎
中使用了机会锁，以最大限度地提高并发和吞吐量。它会使用尽可能多的
RAM
（内存）
作为缓存，并尝试为查询自动选择正确的索引。总之，
MongoDB
的每个方面都是为了保
持高性能而设计的。
尽管
MongoDB
功能强大并且融合了关系数据库的许多特性
，但它的设计初衷并不是具备
关系数据库的所有功能。对于某些功能，数据库服务器会将处理和逻辑交给客户端（由驱
动程序或用户的应用程序代码处理）。这种新型的设计方式是
MongoDB
能够实现如此高性
能的原因之一。
1.5
设计理念
本书会详细阐述
MongoDB
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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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.