Couchbase Server, originally known as Membase, is an open-source, distributed (shared-nothing architecture) NoSQL document-oriented database that is optimized for interactive applications. These applications must serve many concurrent users by creating, storing, retrieving, aggregating, manipulating and presenting data. In support of these kinds of application needs, Couchbase is designed to provide easy-to-scale key-value or document access with low latency and high sustained throughput. It is designed to be clustered from a single machine to very large-scale deployments spanning many machines.
For those familiar with memcached, Couchbase Server provides on-the-wire client protocol compatibility, but is designed to add disk persistence, data replication, live cluster reconfiguration, rebalancing and multitenancy with data partitioning.
In the parlance of Eric Brewer’s CAP theorem, Couchbase is a CP type system meaning it provides consistency and partition tolerance.