Apache HBase:

Apache HBase is an open source column-oriented database built to run on top of the Hadoop Distributed File System (HDFS). Hadoop is a framework for handling large datasets in a distributed computing environment.

HBase is designed to support high table-update rates and to scale out horizontally in distributed compute clusters. Its focus on scale enables it to support very large database tables -- for example, ones containing billions of rows and millions of columns.
Much like Hadoop, an important aspect of the HBase architecture is the use of master nodes to manage region servers that distribute and process parts of data tables. One of the most prominent uses today of HBase is as a structured data handler for Facebook's basic messaging infrastructure.