Non-relational Database Management Systems

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. They use a variety of data models, including document, graph, key-value, in-memory, and search. This page includes resources to help you better understand NoSQL databases and to get started.

How Does a NoSQL (nonrelational) Database Work?

NoSQL databases use a variety of data models for accessing and managing data, such as document, graph, key-value, in-memory, and search. 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 (such as document, key-value, and graph) 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.

What are the types of NoSQL Databases?

• 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.
• 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.
• 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.
• 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 ElastiCache offers Memcached and Redis, to serve low-latency, high-throughput workloads, such as McDonald’s, that cannot be served with disk-based data stores.
• Search: Many applications output logs to help developers troubleshoot issues.