Introduction to MongoDB
MongoDB简介
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Welcome to the MongoDB 4.4 Manual!欢迎使用MongoDB 4.4手册！MongoDB is a document database designed for ease of development and scaling.MongoDB是为便于开发和扩展而设计的文档数据库。The Manual introduces key concepts in MongoDB, presents the query language, and provides operational and administrative considerations and procedures as well as a comprehensive reference section.该手册介绍了MongoDB中的关键概念，介绍了查询语言，并提供了操作和管理注意事项和过程，以及全面的参考部分。
MongoDB offers both a Community and an Enterpriseversion of the database:MongoDB提供了数据库的社区版本和企业版本：
MongoDB Community is the source available and free to useedition of MongoDB.MongoDB社区是MongoDB的免费版本。MongoDB Enterprise is available as part of the MongoDB Enterprise Advanced subscription and includes comprehensive support for your MongoDB deployment.MongoDB Enterprise是MongoDB Enterprise高级订阅的一部分，包括对MongoDB部署的全面支持。MongoDB Enterprise also adds enterprise-focused features such as LDAP and Kerberos support, on-disk encryption, and auditing.MongoDB企业版还添加了面向企业的特性，如LDAP和Kerberos支持、磁盘加密和审计。
Document Database文档数据库
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A record in MongoDB is a document, which is a data structure composed of field and value pairs.MongoDB中的记录是一个文档，它是由字段和值对组成的数据结构。MongoDB documents are similar to JSON objects.MongoDB文档类似于JSON对象。The values of fields may include other documents, arrays, and arrays of documents.字段的值可以包括其他文档、数组和文档数组。
The advantages of using documents are:使用文档的优点是：
Documents (i.e. objects) correspond to native data types in many programming languages.文档（即对象）对应于许多编程语言中的原生数据类型。Embedded documents and arrays reduce need for expensive joins.嵌入式文档和数组减少了对昂贵连接的需要。Dynamic schema supports fluent polymorphism.动态模式支持fluent多态性。
Collections/Views/On-Demand Materialized Views集合/视图/按需物化视图
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MongoDB stores documents in collections.MongoDB将文档存储在集合中。Collections are analogous to tables in relational databases.集合类似于关系数据库中的表。
In addition to collections, MongoDB supports:除了集合，MongoDB还支持：
Read-only只读Views视图(Starting in MongoDB 3.4)（从MongoDB 3.4开始）-
On-Demand Materialized Views随需应变的物化视图(Starting in MongoDB 4.2).（从MongoDB 4.2开始）。
Key Features主要特点
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High Performance高性能
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MongoDB provides high performance data persistence.MongoDB提供了高性能的数据持久性。In particular,具体来说，
Support for embedded data models reduces I/O activity on database system.对嵌入式数据模型的支持减少了数据库系统上的I/O活动。Indexes support faster queries and can include keys from embedded documents and arrays.索引支持更快的查询，并且可以包含来自嵌入文档和数组的键。
Rich Query Language丰富的查询语言
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MongoDB supports a rich query language to supportMongoDB支持丰富的查询语言，以支持
read and write operations (CRUD)读写操作（CRUD）as well as:以及
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Data Aggregation数据聚合 Text Searchand Geospatial Queries.文本搜索和地理空间查询。
See also另请参阅
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SQL to MongoDB Mapping ChartMongoDB映射到图表的SQL -
SQL to Aggregation Mapping Chart聚合映射图表的SQL Learn about the latest query language features with the MongoDB Query Language: What’s Newpresentation from MongoDB.live 2020.了解MongoDB查询语言的最新查询语言特性：MongoDB查询语言：新增内容，展示自MongoDB.live 2020。
High Availability高可用性
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MongoDB’s replication facility, called replica set, provides:MongoDB的复制工具称为副本集，它提供：
automaticfailover自动故障data redundancy.数据冗余。
A replica setis a group of MongoDB servers that maintain the same data set, providing redundancy and increasing data availability.副本集是一组维护相同数据集的MongoDB服务器，提供冗余并提高数据可用性。
Horizontal Scalability横向可扩展性
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MongoDB provides horizontal scalability as part of its corefunctionality:MongoDB提供水平可扩展性作为其核心功能的一部分：
Sharding distributes data across a cluster of machines.分片将数据分布在一组机器上。Starting in 3.4, MongoDB supports creating zones of data based on the shard key.从3.4开始，MongoDB支持基于shard key创建数据区域。In a balanced cluster, MongoDB directs reads and writes covered by a zone only to those shards inside the zone.在平衡集群中，MongoDB只将区域覆盖的读写操作定向到该区域内的那些碎片。See the Zones manual page for more information.有关详细信息，请参阅区域手册页面。
Support for Multiple Storage Engines支持多个存储引擎
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MongoDB supports
multiple storage engines:MongoDB支持
多种存储引擎：
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WiredTiger Storage EngineWiredTiger存储引擎(including support for Encryption at Rest)（包括支持静态加密） -
In-Memory Storage Engine内存存储引擎.
In addition, MongoDB provides pluggable storage engine API that allows third parties to develop storage engines for MongoDB.此外，MongoDB还提供了可插拔的存储引擎API，允许第三方为MongoDB开发存储引擎。