Shared nothing architecture - AbsoluteAstronomy.com

A shared nothing architecture (SN) is a distributed computing

Distributed computing

Distributed computing is a field of computer science that studies distributed systems. A distributed system consists of multiple autonomous computers that communicate through a computer network. The computers interact with each other in order to achieve a common goal...

architecture in which each node is independent and self-sufficient, and there is no single point of contention across the system. More specifically, none of the nodes share memory or disk storage.

People typically contrast SN with systems that keep a large amount of centrally-stored state

State (computer science)

In computer science and automata theory, a state is a unique configuration of information in a program or machine. It is a concept that occasionally extends into some forms of systems programming such as lexers and parsers....

information, whether in a database

Database

A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...

, an application server

Application server

An application server is a software framework that provides an environment in which applications can run, no matter what the applications are or what they do...

, or any other similar single point of contention. While SN is best known in the context of web

World Wide Web

The World Wide Web is a system of interlinked hypertext documents accessed via the Internet...

development, the concept predates the web: Michael Stonebraker

Michael Stonebraker

Michael Ralph Stonebraker is a computer scientist specializing in database research.Through a series of academic prototypes and commercial startups, Stonebraker's research and products are central to many relational database systems on the market today...

at the University of California, Berkeley

University of California, Berkeley

The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

used the term in a 1986 database paper. In it he mentions existing commercial implementations of the architecture (although none are named explicitly). Teradata

Teradata

Teradata Corporation is a vendor specializing in data warehousing and analytic applications. Its products are commonly used by companies to manage data warehouses for analytics and business intelligence purposes. Teradata was formerly a division of NCR Corporation, with the spinoff from NCR on...

, which delivered its first system in 1983, was probably one of those commercial implementations.

Shared nothing is popular for web development because of its scalability

Scalability

In electronics scalability is the ability of a system, network, or process, to handle growing amount of work in a graceful manner or its ability to be enlarged to accommodate that growth...

. As Google

Google

Google Inc. is an American multinational public corporation invested in Internet search, cloud computing, and advertising technologies. Google hosts and develops a number of Internet-based services and products, and generates profit primarily from advertising through its AdWords program...

has demonstrated, a pure SN system can scale almost infinitely simply by adding nodes in the form of inexpensive computers, since there is no single bottleneck to slow the system down. Google calls this sharding. An SN system typically partitions its data among many nodes on different databases (assigning different computers to deal with different users or queries), or may require every node to maintain its own copy of the application's data, using some kind of coordination protocol. This is often referred to as database sharding.

There is some doubt about whether a web application with many independent web nodes but a single, shared database (clustered or otherwise) should be counted as SN. One of the approaches to achieve SN architecture for stateful applications (which typically maintain state in a centralized database

Centralized database

A Centralized database is a database located and maintained in one location, unlike a distributed database. One main advantage is that all data is located in one place. The disadvantage is that bottlenecks may occur....

) is the use of a data grid, also known as distributed caching. This still leaves the centralized database as a single point of failure.

Shared nothing architectures have become prevalent in the data warehousing space. There is much debate as to whether the shared nothing approach is superior to shared Disk with sound arguments presented by both camps. Shared nothing architectures certainly take longer to respond to queries that involve joins over large data sets from different partitions (machines). However the potential for scaling is huge.

What Is Shared

While there is no single point of contention within the software/hardware components of SN systems, it should be noted that information from disparate nodes still needs to be reintegrated at some point. Such points occur wherever an information system that is outside the SN architecture queries information from disparate nodes within the SN architecture for a single purpose. Examples of such external nodes might be:

persons (minds) who look at two SN nodes and decide that they hold or process data about the same thing (simply recognising that two nodes belong to the same SN system would be sufficient)
any software/hardware system that is written to query different nodes within the SN architecture

What Is Shared

See also