Cassandra is a NoSQL database designed by Facebook to manage large amounts of structured data across hundreds of nodes with high write throughput using cheap hardware. It provides high scalability, reliability and performance. Cassandra uses a decentralized architecture with consistent hashing to partition and replicate data across multiple nodes. It has a simple API with insert, get, and delete methods. Facebook successfully uses Cassandra to power their inbox search with over 50 TB of data distributed across 150 nodes in different datacenters, achieving millisecond read latencies at scale.