Introduction to NoSQL by Martin Fowler. MongoDB Tutorial. Sans titre. Because of the way they are structured, relational databases usually scale vertically – a single server has to host the entire database to ensure acceptable performance for cross- table joins and transactions.
This gets expensive quickly, places limits on scale, and creates a relatively small number of failure points for database infrastructure. The solution to support rapidly growing applications is to scale horizontally, by adding servers instead of concentrating more capacity in a single server. "Sharding" a database across many server instances can be achieved with SQL databases, but usually is accomplished through SANs and other complex arrangements for making hardware act as a single server.
Because the database does not provide this ability natively, development teams take on the work of deploying multiple relational databases across a number of machines. Data is stored in each database instance autonomously. NoSQL. "Structured storage" redirects here.
For the Microsoft technology also known as structured storage, see COM Structured Storage. A NoSQL (originally referring to "non SQL" or "non relational" ) database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed since the late 1960s, but did not obtain the "NoSQL" moniker until a surge of popularity in the early twenty-first century, triggered by the needs of Web 2.0 companies such as Facebook, Google and Amazon.com. Motivations for this approach include: simplicity of design, simpler "horizontal" scaling to clusters of machines, which is a problem for relational databases, and finer control over availability. History Types and examples of NoSQL databases There have been various approaches to classify NoSQL databases, each with different categories and subcategories, some of which overlap.
Not ACID. In 1983, Andreas Reuter and Theo Härder coined the acronym ACID to describe them. Characteristics The characteristics of these four properties as defined by Reuter and Härder: Atomicity Consistency Isolation Durability Examples The following examples further illustrate the ACID properties.
Distributed transaction - difficult for both SQL and NoSQL. A distributed transaction is a database transaction in which two or more network hosts are involved.
Usually, hosts provide transactional resources, while the transaction manager is responsible for creating and managing a global transaction that encompasses all operations against such resources. Distributed transactions, as any other transactions, must have all four ACID (atomicity, consistency, isolation, durability) properties, where atomicity guarantees all-or-nothing outcomes for the unit of work (operations bundle). Open Group, a vendor consortium, proposed the X/Open Distributed Transaction Processing (DTP) Model (X/Open XA), which became a de facto standard for behavior of transaction model components. Real-time web. The real-time web is a network web using technologies and practices that enable users to receive information as soon as it is published by its authors, rather than requiring that they or their software check a source periodically for updates.
Difference from real-time computing The real-time web is fundamentally different from real-time computing since there is no knowing when, or if, a response will be received. The information types transmitted this way are often short messages, status updates, news alerts, or links to longer documents. The content is often "soft" in that it is based on the social web—people's opinions, attitudes, thoughts, and interests—as opposed to hard news or facts. True-realtime web (an "alternate" model) From another point of view, the real-time web consists in making the client interface (or the web side; or the web layer) of a web application, to communicate continuously with the corresponding real-time server, during every user connection.
Scalability. Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate that growth. For example, it can refer to the capability of a system to increase its total output under an increased load when resources (typically hardware) are added.
An analogous meaning is implied when the word is used in an economic context, where scalability of a company implies that the underlying business model offers the potential for economic growth within the company. Scalability, as a property of systems, is generally difficult to define and in any particular case it is necessary to define the specific requirements for scalability on those dimensions that are deemed important. Why are Relational Databases “Relational”? Many people wonder why relational databases are called “relational.”
Some think that it’s because of a logical entity-relationship model you often start your design with. Or, because you have tables and relationships (aka foreign keys) between them. But that’s not the case. The name comes from the mathematical notion of “relation.” It all started with E.