Shared-nothing

A shared nothing architecture (SN) is a distributed computing 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 information, whether in a database, an application server, or any other similar single point of contention.

The advantages of SN architecture versus a central entity that controls the network (a controller-based architecture) include eliminating any single point of failure, allowing self-healing capabilities and providing an advantage with offering non-disruptive upgrade.

While SN is best known in the context of web development, the concept predates the web: Michael Stonebraker at the University of California, Berkeley used the term in a 1986 database paper. In it he mentions existing commercial implementations of the architecture (although none are named explicitly). Teradata, which delivered its first system in 1983, was probably one of those commercial implementations.Tandem Computers officially released NonStop SQL, a shared nothing database, in 1984.

Shared nothing is popular for web development because of its scalability. As Google has demonstrated, a pure SN system can scale hugely 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. A 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.

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