Apache HBase is an open-source, distributed, versioned, non-relational database
modeled after Google's Bigtable: A Distributed Storage System for Structured
Data by Chang et al.  Just as Bigtable leverages the distributed data storage
provided by the Google File System, Apache HBase provides Bigtable-like
capabilities on top of Hadoop and HDFS.

Features:
-- Linear and modular scalability
-- Strictly consistent reads and writes
-- Automatic and configurable sharding of tables
-- Automatic failover support between RegionServers
-- Convenient base classes for backing Hadoop MapReduce jobs with
   Apache HBase tables
-- Easy to use Java API for client access
-- Block cache and Bloom Filters for real-time queries
-- Query predicate push down via server side Filters
-- Thrift gateway and a REST-ful Web service that supports XML, Protobuf
   and binary data encoding options
-- Extensible jruby-based (JIRB) shell
-- Support for exporting metrics via the Hadoop metrics subsystem to files
   or Ganglia, or via JMX

WWW: http://hbase.apache.org/