What is NoSQL?

High-performance, nonrelational databases with flexible data models

What are NoSQL databases?

NoSQL databases are purpose built for specific data models and have flexible schemas for building modern applications. NoSQL databases are widely recognized for their ease of development, functionality, and performance at scale. This page includes resources to help you better understand NoSQL databases and to get started.

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How Does a NoSQL (nonrelational) Database Work?

NoSQL databases use a variety of data models for accessing and managing data. These types of databases are optimized specifically for applications that require large data volume, low latency, and flexible data models, which are achieved by relaxing some of the data consistency restrictions of other databases.

Consider the example of modeling the schema for a simple book database:

  • In a relational database, a book record is often dissembled (or "normalized") and stored in separate tables, and relationships are defined by primary and foreign key constraints. In this example, the Books table has columns for ISBN, Book Title, and Edition Number, the Authors table has columns for AuthorID and Author Name, and finally the Author-ISBN table has columns for AuthorID and ISBN. The relational model is designed to enable the database to enforce referential integrity between tables in the database, normalized to reduce the redundancy, and generally optimized for storage.
  • In a NoSQL database, a book record is usually stored as a JSON document. For each book, the item, ISBN, Book Title, Edition Number, Author Name, and AuthorID are stored as attributes in a single document. In this model, data is optimized for intuitive development and horizontal scalability.

Why should you use a NoSQL database?

NoSQL databases are a great fit for many modern applications such as mobile, web, and gaming that require flexible, scalable, high-performance, and highly functional databases to provide great user experiences.

  • Flexibility: NoSQL databases generally provide flexible schemas that enable faster and more iterative development. The flexible data model makes NoSQL databases ideal for semi-structured and unstructured data.
  • Scalability: NoSQL databases are generally designed to scale out by using distributed clusters of hardware instead of scaling up by adding expensive and robust servers. Some cloud providers handle these operations behind-the-scenes as a fully managed service.
  • High-performance:NoSQL database are optimized for specific data models and access patterns that enable higher performance than trying to accomplish similar functionality with relational databases.
  • Highly functional: NoSQL databases provide highly functional APIs and data types that are purpose built for each of their respective data models.

Types of NoSQL Databases

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Key-value: Key-value databases are highly partitionable and allow horizontal scaling at scales that other types of databases cannot achieve. Use cases such as gaming, ad tech, and IoT lend themselves particularly well to the key-value data model. Amazon DynamoDB is designed to provide consistent single-digit millisecond latency for any scale of workloads. This consistent performance is a big part of why the Snapchat Stories feature, which includes Snapchat's largest storage write workload, moved to DynamoDB.

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Document: In application code, data is represented often as an object or JSON-like document because it is an efficient and intuitive data model for developers. Document databases make it easier for developers to store and query data in a database by using the same document model format that they use in their application code. The flexible, semistructured, and hierarchical nature of documents and document databases allows them to evolve with applications' needs. The document model works well with catalogs, user profiles, and content management systems where each document is unique and evolves over time. Amazon DocumentDB (with MongoDB compatibility) and MongoDB are popular document databases that provide powerful and intuitive APIs for flexible and iterative development.

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Graph: A graph database's purpose is to make it easy to build and run applications that work with highly connected datasets. Typical use cases for a graph database include social networking, recommendation engines, fraud detection, and knowledge graphs. Amazon Neptune is a fully-managed graph database service. Neptune supports both the Property Graph model and the Resource Description Framework (RDF), providing the choice of two graph APIs: TinkerPop and RDF/SPARQL. Popular graph databases include Neo4j and Giraph.

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In-memory: Gaming and ad-tech applications have use cases such as leaderboards, session stores, and real-time analytics that require microsecond response times and can have large spikes in traffic coming at any time. Amazon MemoryDB for Redis is a Redis-compatible, durable, in-memory database service that delivers microsecond read latency, single-digit millisecond write latency, and Multi-AZ durability. MemoryDB is purpose-built to deliver ultra-fast performance and durability so you can use it as your primary database for modern, microservices applications. Amazon ElastiCache is a fully managed, in-memory caching service compatible with both Redis and Memcached, to serve low-latency, high-throughput workloads. Customers like Tinder, who require real-time response from their applications, rely on in-memory data stores rather than disk-based data stores. Amazon DynamoDB Accelerator (DAX) is another example of a purpose-built data store. DAX makes DynamoDB reads an order of magnitude faster.

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Search: Many applications output logs to help developers troubleshoot issues. Amazon Elasticsearch Service (Amazon ES) is purpose built for providing near-real-time visualizations and analytics of machine-generated data by indexing, aggregating, and searching semistructured logs and metrics. Amazon ES also is a powerful, high-performance search engine for full-text search use cases. Expedia is using more than 150 Amazon ES domains, 30 TB of data, and 30 billion documents for a variety of mission-critical use cases, ranging from operational monitoring and troubleshooting to distributed application stack tracing and pricing optimization.

SQL (relational) vs. NoSQL (nonrelational) databases

For decades, the predominant data model that was used for application development was the relational data model used by relational databases such as Oracle, DB2, SQL Server, MySQL, and PostgreSQL. It wasn't until the mid to late 2000s that other data models began to gain significant adoption and usage. To differentiate and categorize these new classes of databases and data models, the term "NoSQL" was coined. Often the term "NoSQL" is used interchangeably with "nonrelational."

Though there are many types of NoSQL databases with varying features, the following table shows some of the differences between SQL and NoSQL databases.

Getting Started with NoSQL

SQL vs. NoSQL Terminology

The following table compares terminology used by select NoSQL databases with terminology used by SQL databases.

SQL MongoDB DynamoDB Cassandra Couchbase
Table Collection Table Table Data bucket
Row Document Item Row Document
Column Field Attribute Column Field
Primary key ObjectId Primary key
 Primary key Document ID
Index Index Secondary index Index Index
View View Global secondary index Materialized view View
Nested table or object Embedded document Map Map Map
Array Array List List List

Get started with DynamoDB