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nosql

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Otávio Santana edited this page Aug 6, 2013 · 1 revision

A NoSQL database provides a mechanism for storage and retrieval of data that uses looser consistency models than traditional relational databases. Motivations for this approach include simplicity of design, horizontal scaling and finer control over availability. NoSQL databases are often highly optimized key–value stores intended for simple retrieval and appending operations, with the goal being significant performance benefits in terms of latency and throughput. NoSQL databases are finding significant and growing industry use in big data and real-time web applications. NoSQL systems are also referred to as "Not only SQL" to emphasize that they do in fact allow SQL-like query languages to be used.

ACID vs BASE NoSQL cannot necessarily give full ACID guarantees. Usually eventual consistency is guaranteed or transactions limited to single data items. This means that given a sufficiently long period of time over which no changes are sent, all updates can be expected to propagate eventually through the system.

The CAP theorem states that a distributed computer system cannot guarantee all of the following three properties at the same time:

  • Consistency
  • Availability
  • Partition tolerance

A BASE system gives up on consistency.

  1. Basically Available indicates that the system does guarantee availability, in terms of the CAP theorem.
  2. Soft state indicates that the state of the system may change over time, even without input. This is because of the eventual consistency model.
  3. Eventual consistency indicates that the system will become consistent over time, given that the system doesn't receive input during that time.

There have been various approaches to classify NoSQL databases, each with different categories and subcategories. Because of the variety of approaches and overlappings regarding the nonfunctional requirements and the feature-set it could be difficult to get and maintain an overview of the nonrelational database market. Nevertheless, the most basic classification that most would agree is one based on the data model. A few of these and their prototypes are:

  • Column: Hbase, Cassandra, Accumulo
  • Document: MongoDB, Couchbase, Raven
  • Key-value: Dynamo, Riak, Azure, Redis, Cache, GT.m
  • Graph: Neo4J, Allegro, Virtuoso, Bigdata

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