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NoSQL Database Guide

What is NoSQL?

NoSQL is a non-relational database that does not typically use Structured Query Language (SQL) to retrieve information. NoSQL databases were developed for use cases where a traditional relational database is not sufficient due to the size (volume), type (variety) or speed (velocity) of big data.

Learn about Scylla and NoSQL at the Scylla University

What is SQL?

Structured Query Language (SQL) is a database management language, and currently the most popular method of accessing data from and inputting data to a relational database management system (RDBMS). SQL databases have been around for decades. First invented in 1974, SQL has continued to evolve over the years. Because it is such an important industry standard, it is controlled by the International Electrotechnical Commission (IEC). The latest version is formally defined in ISO/IEC 9075:2016.

SQL databases are comprised of records organized into tables. In a single table, data is organized into rows, labeled with a primary key, and with many columns (columnar databases) to hold values for different kinds of data – typically large data sets. These tables are related to each other through the use of foreign keys, which join together the different tables in the database.

A schema is used to define all of the tables, their composite columns and data types, and the means of joining the tables together. The structure of a relational database can be illustrated by a design referred to as an Entity Relationship Diagram (ERD).

Diagram depicting an Entity Relationship Diagram commonly used to model data in SQL RDBMS vs NoSQL
Figure 1: An example of a typical Entity Relationship Diagram (ERD) used to model data in a SQL RDBMS; note that the tables are joined using various relationships (these symbols are called “crow’s foot” notations)

What's the Difference Between SQL and NoSQL?

What is a NoSQL Database?

A NoSQL database (NoSQL DB) is designed to handle massive amounts of distributed data. NoSQL database management systems store and retrieve data in a variety of ways other than the joined tabular models of relational database management systems (RDBMS). These databases can handle different types of data and can accommodate many kinds of data models including key-value stores, document, wide-column and graph formats.

The advantages of using them are for modern applications that need fast horizontal scaling and for those with extremely large, high velocity, distributed datasets. Fully managed NoSQL DBaaS solutions are increasing in popularity for use cases where a team of experts is needed to manage the complexity and upkeep of such databases. 

NoSQL Database History

The term “NoSQL” was coined by Carlo Strozzi in 1998. He had invented a form of RDBMS that used a different form of data access than SQL. Note that his database was still a relational database — tables still had joins — but the method of accessing it, using Unix pipes, did not rely on the SQL language.

Modern versions came about a decade later with the advent of massive Internet e-commerce platforms and social media. While in the early Internet and web era many SQL databases were adapted for data applications (such as the use of open source MySQL to power WordPress sites), there were architectural limitations to SQL servers that made it too inflexible and unscalable for entire new classes of problems that needed to be solved. New data models were required. These included massive (but relatively simple) key value stores, highly distributed and highly available wide column stores, and more unique data models such as document based stores and graph databases.

Sometimes they are also referred to as “Not only SQL” or “NewSQL” to show that they may actually support Structured Query Language or can work in tandem with a SQL database. A SQL-based interface can still be useful, and these databases support hybrid operations, doing both SQL and Non-SQL related data management.

NoSQL and NewSQL: A Comparison of Distributed Database Systems

In this whitepaper, we provide an expansive comparison of NoSQL databases against distributed SQL (“NewSQL”) databases. You will learn the architectural differences between NoSQL and NewSQL, YCSB benchmark results for leading NoSQL and NewSQL databases such as Scylla and CockroachDB, and much more.

NoSQL and NewSQL: A Comparison of Distributed Database Systems

NoSQL Tutorial: Wide Column Store NoSQL vs SQL Data Modeling

What are NoSQL Databases Used For?

Many types of NoSQL databases are used for applications with very large datasets and some operate in real time. They are used by enterprises that need features and capabilities more flexible than a traditional database, which can accommodate many kinds of data models in a variety of formats (flexible). These databases provide the following data management features not found in relational databases:

  • Caching — Improves application response when the same information is being sent to many users. NoSQL storage of data provides a solution without having to maintain a custom cache.
  • Highly available, globally-distributed data — With worldwide user bases and demanding requirements for always-on services, data systems cannot just reside in a single internal datacenter. Many support global distribution of servers and automatic replication of data between them. This is called Cross Datacenter Replication.
  • Fast access for big data — NoSQL software can handle the massive amounts of data in today’s systems quicker and with less cost than relational databases. “Fast” is often qualified in two ways: latency, which measures the speed of response times, often measured in the range of milliseconds or sub-milliseconds, as well as throughput, which measures the raw amount of data that can be processed, often measured in operations-per-second.
  • Consistency — The consistency requirements of many NoSQL databases use cases are less rigid than for relational databases. For instance, when handling ephemeral, transient, rapidly-changing data. In such cases, some data loss is acceptable to maintain system availability. Today, the ACID model is not always necessary when an “eventual consistency” model promotes better performance. Some offer a range of consistency levels to choose from, including “tunable consistency,” where every database transaction may have its own consistency level.

Why Use NoSQL Databases?

The flexible architecture of NoSQL databases is among the top reasons why they are an excellent choice for today’s demanding application requirements. Other advantages for when to use NoSQL are as follows:

  • Easier scalability — Can be easily scaled to handle massive amounts of data. Their distributed nature means increases in demand can be met by simply adding servers to the cluster.
  • More efficiency — The looser data consistency models of NoSQL databases can result in better efficiency. When new information doesn’t have to be updated across the entire database in real time, resources can be directed to more critical issues.
  • Simple documents — Document-oriented NoSQL databases store data as simple documents, which leads to easier data manipulation than the data mapping required in SQL databases.
  • Always on — The distributed nature allows them to always remain on for enterprises that require non-stop service.

SQL Database Examples

Db2IBM’s relational database, originally released in 1983 and created to run on mainframes; over time it was also ported to Unix and Windows; now supports Linux servers.
MariaDBAn open source SQL server, forked from MySQL; was created in 2009 when MySQL was acquired by Oracle.
MemSQLA distributed SQL server designed to run from memory (RAM) for fastest performance.
Microsoft SQL ServerMicrosoft’s SQL server, originally designed to run on OS/2, became the mainstay of databases to run on Microsoft Operating Systems. In 2017 it was ported to run on Linux.
MySQLAn open source SQL server widely adopted by web and application developers. In 2008 it was acquired by Oracle; now available as both open source and proprietary enterprise editions.
OracleFirst released in 1979, Oracle became and remains widely adopted in enterprises over the next decades.
PostgreSQLAn open source SQL server that grew out of, and eventually replaced, the 1980s Ingres project at UC Berkeley.

Is There a Free NoSQL Database?

In general, this type of database has active communities of developers who contribute to open source, and thus technically offering free NoSQL databases. Many of these also provide a commercial, enterprise NoSQL database that add additional features, as well as production support. A free NoSQL database typically only provides community support, with no guarantee that issues will be fixed or new features added in a timely fashion. Small projects can generally begin development on a free open source NoSQL database, and then upgrade to an enterprise version once the project achieves traction.

Free NoSQL is typically available to run locally, on a developer’s machine but also can be hosted and managed in the cloud. Many NoSQL database providers also provide free NoSQL hosting that runs in the cloud as database-as-a-service (NoSQL DBaaS) offerings. Developers can easily find a free NoSQL database online as well as free NoSQL database hosting from a range of providers.

Using SQL and NoSQL Together

Modern enterprises do not view SQL and NoSQL as an either/or proposition. A survey at the latest DeveloperWeek conference found that 44 percent of organizations use multiple databases. Among those, 75 percent use a combination of SQL and NoSQL databases.

Many organizations take advantage of the ways that these two databases can complement each other. Each brings its own strengths, making the sum greater than each part.

SQL databases handle structured data and standardize how elements relate to one another. NoSQL databases are popular when flexibility is a concern. They can create unique data structures that include documents, graphs or columns.

How is NoSQL Data Modeled in a NoSQL Database?

Schemas are often exhibit a more flexible design without enforcing the normalized data forms and pre-defined schemas and structures common in SQL databases.

One benefit is the ability to easily transition from simple key-value stores to complicated graph databases when integrated with a graph database.

Since this is an emerging technology, solutions for NoSQL data modeling are still being developed. As more enterprises utilize NoSQL database features, the design will mature with the following benefits:

  • Reusable data model design patterns for more efficient application development.
  • An inventory of unified NoSQL data models that can support different NoSQL products.
  • Automated data model extraction from application source code.
  • Automated code-model-data consistency validation.
  • Strong control for application and data model change management.

Learn the Difference Between Data Modelling for NoSQL and Data Modelling for SQL

Are NoSQL Databases Faster than SQL Databases?

Key-value systems often have far simpler schemas, and thus, they tend to be faster than SQL systems. SQL databases tend to allow for more complex queries, exemplified by making JOINs across tables. Naturally, there is a computational cost, and time required, for such complexity. There are many additional architectural factors that go into a specific database’s performance, such as the use of in-memory tables or RAM caches, various data structures that can help efficiency (such as bloom filters) and so on. Even the programming language a database is written in can affect system performance, as it may allow for, or prohibit, low-level hardware optimization. Thus it is not possible to categorically say that NoSQL databases are always faster than SQL databases (or vice versa). Users need to create and conduct realistic tests to see how various databases perform under specific conditions, data models, and querying patterns.

How are NoSQL Databases Indexed?

They are indexed with keys that correspond with the location of an associated piece of data. The most common indexing methods are B-Tree, T-Tree, O2-Tree, as well as Log Structured Merge (LSM) tree indexing.

  • B-Tree Indexing

    — Allows a variable number of child nodes, which results in more unused space and less tree balancing. The B+Tree is a popular version of B-Tree indexing where every key must reside in the leaves.

  • T-Tree Indexing

    — Features three kinds of nodes: A T-Node that has a right and left child, a leaf node with no children, and a half-leaf node with only one child. Each node stores multiple tuples, or lists. The use of binary search results in more efficient storage.

  • O2-Tree Indexing

    — Created to enhance existing indexing methods by placing tuples within each leaf node. Advances the concept of a Binary-Search tree.

  • Log Structured Merge (LSM) Tree Indexing

    — Creates an in-memory hash table (or memtable), and periodically write these structures to disk in immutable form, known as a Sorted Strings Table (SSTable). Over time, these SSTables are merged in a process known as compaction.

NoSQL Database Examples / NoSQL Database List

The NoSQL database examples include the following:

DatabaseNoSQL Data ModelsDescription
AerospikeKey-valueA flash-optimized and in-memory open source NoSQL database
Amazon DynamoDB Key-value, DocumentCloud-based database only offered on AWS
Apache CassandraColumn
Time series
An open source highly scalable and distributed database created at Facebook to handle massive amounts of structured data.
Apache CouchDBDocumentOpen source and web-oriented database.
Apache HBaseColumnOpen source and column store database developed as a part of Hadoop.
Google BigtableColumnA compressed, high performance, proprietary data storage system.
JanusGraphGraphAn open source, distributed graph database under The Linux Foundation; works on top of Scylla or Apache Cassandra.
Microsoft Cosmos DBDocument
Columnar
Graph
Proprietary, schema-agnostic and horizontally scalable.
MongoDBDocumentDocument-oriented database by MongoDB.
Neo4jGraphACID-compliant and transactional graph database with native graph storage and processing.
Oracle NoSQL DatabaseKey-valueScalable, distributed NoSQL database, designed to provide highly reliable, flexible and available data management.
RedisKey-value
Document
Time series
Data structure server with keys can contain strings, hashes, lists, sets and sorted sets.
ScyllaKey-value
Column
Time series
Enterprise and open source database which is a drop-in alternative to Apache Cassandra offering higher performance, lower latency and reduced cost.

Learn the Benefits of Migrating to NoSQL and Key Differences you should prepare for Migration