Apache Cassandra, a top level Apache project born at Facebook and built on Amazon’s Dynamo and Google’s BigTable, is a distributed database for managing large amounts of structured data across many commodity servers, while providing highly available service and no single point of failure.  Cassandra offers capabilities that relational databases and other NoSQL databases simply cannot match such as: continuous availability, linear scale performance, operational simplicity and easy data distribution across multiple data centers and cloud availability zones.Ring Architecture

Cassandra’s architecture is responsible for its ability to scale, perform, and offer continuous uptime. Rather than using a legacy master-slave or a manual and difficult-to-maintain sharded architecture, Cassandra has a masterless “ring” design that is elegant, easy to setup, and easy to maintain.

In Cassandra, all nodes play an identical role; there is no concept of a master node, with all nodes communicating with each other equally. Cassandra’s built-for-scale architecture means that it is capable of handling large amounts of data and thousands of concurrent users or operations per second—​even across multiple data centers—​as easily as it can manage much smaller amounts of data and user traffic. Cassandra’s architecture also means that, unlike other master-slave or sharded systems, it has no single point of failure and therefore is capable of offering true continuous availability and uptime — simply add new nodes to an existing cluster without having to take it down.

Many companies have successfully deployed and benefited from Apache Cassandra including some large companies such as: AppleComcast,InstagramSpotifyeBayRackspaceNetflix, and many more. The larger production environments have PB’s of data in clusters of over 75,000 nodes. Cassandra is available under the Apache 2.0 license.