A highly scalable, eventually consistent, distributed, structured key-value store.
The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
Cassandra was open sourced by Facebook in 2008, where it was designed by one of the authors of Dynamo. In a lot of ways you can think of Cassandra as Dynamo 2.0. Cassandra is in production use at Rackspace, Digg, and a number of other companies, but is still under heavy development.
The latest release is 0.4.2 (Changes)
Writes never fail. Two different read paths are available: high-performance "weak" reads and quorum reads. See ThriftInterface.
Every node in the cluster is identical. There are no network bottlenecks. There are no single points of failure.
Cassandra follows the "eventually consistent" model but includes sophisticated features such as Hinted Handoff and Read Repair to minimize inconsistency windows.
Data is automatically replicated to multiple nodes for fault-tolerance. There is support for implementing strategies that replicate across multiple data centers.
Allowing efficient use for many applications beyond simple key/value.
Cassandra guarantees reads and writes to be atomic within a single ColumnFamily.
Storage and throughput increase linearly as new nodes are added. If you need more capacity, simply add more nodes.
Many of the Cassandra developers and community members hang out in the #cassandra channel on irc.freenode.net.
If you are new to IRC and don't have a client, you can use a web-based client.