In the distributed traversal engine model, a traversal is represented as a flow of messages between elements of the graph. Generally, each element (e.g. vertex) is operating independently of the other elements. Each element is seen as its own processor with its own (usually homogenous) program to execute. Elements communicate with each other via message passing. When no more messages have been passed, the traversal is complete and the results of the traversal are typically represented as a distributed data structure over the elements. Graph databases of this nature tend to use the Bulk Synchronous Parallel model of distributed computing. Each step is synchronized in a manner analogous to a clock cycle in hardware. Instances of this model include Agrapa, Pregel, Trinity, GoldenOrb, and others.
None of these graph databases offers distributed traversal engines.
Original title and link: Graph Databases: Distributed Traversal Engine (NoSQL databases © myNoSQL)