May 2024
Intermediate
278 pages
5h 24m
Chinese
Content preview from 构建可扩展分布式系统：方法与实践
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.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.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.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.
174
｜
第
10
章
集合中的每个对象都不需要具有相同的格式。
关于这种灵活性，不可避免的代价是应用程序有责任解析它读取的数据的结构，需要将
数据对象与元数据（用于解析结构，基本上是字段名称）一起存储在数据库中。你经常
会看到这两种方法，即写时模式（
schema-on-write
，定义模式）和读时模式（
schema-on-
read
，无模式）。
10.3.2
查询语言
NoSQL
数据库查询语言几乎总是特定数据库专有的，并且与基于显式
API
和类似
SQL
的声明性语言有所不同。由供应商和第三方实现的支持不同语言的客户端库可供应用
程序使用。例如，
MongoDB
官方支持针对不同语言的
12
个客户端库（
https://oreil.
ly/1xJfN
），并且还有更多的第三方产品（
https://oreil.ly/GxWb2
）。
键值数据库可能只提供支持基于单个键值的
CRUD
操作的
API
。文档数据库通常支持单
个文档字段的索引。这使得检索结果集和更新文档等查询能够高效实现，并满足不同的
文档搜索标准。例如，以下是一个
MongoDB
查询，它从滑雪者数据库文档集合中检索
所有
16
岁以上未更新滑雪通行证的个人：
db.skiers.find( {
age: { $gt: 16},
renew: { $exists: false }}
)
列存储数据库具有多种查询功能。
HBase
支持
Java CRUD API
（
https://oreil.ly/VwMCo
），
使用过滤器检索结果集。
CQL
（
Cassandra
查询语言）以
SQL
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
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.