Cassandra

The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance. Linear scalability and proven fault-tolerance on commodity hardware or cloud infrastructure make it the perfect platform for mission-critical data. Cassandra's support for replicating across multiple datacenters is best-in-class, providing lower latency for your users and the peace of mind of knowing that you can survive regional outages.

Distributed

Every node in the cluster has the same role. There is no single point of failure. Data is distributed across the cluster
(so each node contains different data), but there is no master as every node can service any request.

Supports replication and multi-data center replication

Replication strategies are configurable.[15] Cassandra is designed as a distributed system, for the deployment of large numbers of nodes across multiple data centers. Key features of Cassandra’s distributed architecture are specifically tailored for multiple-data center deployment, for redundancy, for failover and disaster recovery.

Scalability

Designed to have read and write throughput both increase linearly as new machines are added, with the aim of no downtime
or interruption to applications.

Fault-tolerant

Data is automatically replicated to multiple nodes for fault-tolerance. Replication across multiple data centers is supported. Failed nodes can be replaced with no downtime.

Tunable consistency

Cassandra is typically classified as an AP system, meaning that availability and partition tolerance are generally
considered to be more important than consistency in Cassandra, Writes and reads offer a tunable level of consistency,
all the way from "writes never fail" to "block for all replicas to be readable", with the quorum level in the middle.

MapReduce support

Cassandra has a Hadoop integration, with MapReduce support. There is support also for Apache Pig and Apache Hive.

Query language

Cassandra introduced the Cassandra Query Language (CQL). CQL is a simple interface for accessing Cassandra, as an
alternative to the traditional Structured Query Language (SQL).