NoSQL databases provide the performance,scalability and stability that’s required by the modern data-driven apps we interact with these days.But that is where the similarity between NoSQL systems end.In fact,it wouldn’t be wrong to say that the only thing most NoSQLdatabases have in common is that they do not follow the traditional relational data model.Broadly speaking,NoSQLdatabases typically fall into one of four categories:
Key-valueThese function in heavy read environments.Key-value stores are the simplest form of NoSQLdatabases and won’t be of much help when there are complex relationships between data elements.That’s because all access to the database is done using a primary key. Redis and Memcached are frequently used solutions.
Columnar These are optimised for reading and writing columns of data as opposed to rows of data. Also known as wide-column store databases, they are well suited for analysing huge data sets. Apache Cassandra, HBase and Accumulo are the best-known ones.
Document These store, manage and retrieve data as semi-structured documents such as JSON and XML. These document-orientated databases store all information for a given object, and each object can be quite different from the others. MongoDB, Couchbase and CouchDB are the best known and most widely used.
Graph Focus on how data relates to other data points. These databases explore the relationships that link data. Data from graph databases stores directed link between data sets called edges. Neo4j,OrientDB and JanusGraph are popular examples.
NoSQL数据库提供了我们现在与之交互的现代数据驱动应用程序所需的性能，可伸缩性和稳定性。但这就是NoSQL系统之间的相似性结束的地方。事实上，说这是唯一的事情并不是错的。大多数NoSQL数据库的共同之处在于它们不遵循传统的关系数据模型。总的来说，NoSQL数据库通常属于以下四类之一：
键值这些重读值环境中的函数。键值存储是NoSQL数据库的最简单形式并且赢了当数据元素之间存在复杂关系时，会有很大帮助。这是因为所有对数据库的访问都是使用主键完成的。 Redis和Memcached是经常使用的解决方案。
Columnar这些针对读取和写入数据列进行了优化，而不是数据行。它们也称为宽列存储数据库，非常适合分析大量数据集。 Apache Cassandra，HBase和Accumulo是最知名的。
Document这些以半结构化文档（如JSON和XML）存储，管理和检索数据。这些面向文档的数据库存储给定对象的所有信息，每个对象可能与其他对象完全不同。 MongoDB，Couchbase和CouchDB是最知名和最广泛使用的。
图表关注数据与其他数据点的关系。这些数据库探索链接数据的关系。来自图数据库的数据存储称为边的数据集之间的有向链接。 Neo4j，OrientDB和JanusGraph是很受欢迎的例子。
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