Apache Giraph is a graph-processing system that uses the MapReduce model to process graphs. Currently, it is in incubation at the Apache Software Foundation.

It is based on Google's Pregel, which is used to calculate page rank.

Currently, Giraph is being used by Facebook, Twitter, and LinkedIn to create social graphs of their users. Both Giraph and Pregel are based on the Bulk Synchronous Parallel (BSP) model of distributed computation, which was introduced by Leslie Valiant.

Support for YARN is from release 1.1.0. For more information, refer to the official site at http://giraph.apache.org/.