public class Pregel extends Object
Unlike the original Pregel API, the GraphX Pregel API factors the sendMessage computation over edges, enables the message sending computation to read both vertex attributes, and constrains messages to the graph structure. These changes allow for substantially more efficient distributed execution while also exposing greater flexibility for graph-based computation.
|Constructor and Description|
|Modifier and Type||Method and Description|
Execute a Pregel-like iterative vertex-parallel abstraction.
public static <VD,ED,A> Graph<VD,ED> apply(Graph<VD,ED> graph, A initialMsg, int maxIterations, EdgeDirection activeDirection, scala.Function3<Object,VD,A,VD> vprog, scala.Function1<EdgeTriplet<VD,ED>,scala.collection.Iterator<scala.Tuple2<Object,A>>> sendMsg, scala.Function2<A,A,A> mergeMsg, scala.reflect.ClassTag<VD> evidence$1, scala.reflect.ClassTag<ED> evidence$2, scala.reflect.ClassTag<A> evidence$3)
vprogis executed in parallel on each vertex receiving any inbound messages and computing a new value for the vertex. The
sendMsgfunction is then invoked on all out-edges and is used to compute an optional message to the destination vertex. The
mergeMsgfunction is a commutative associative function used to combine messages destined to the same vertex.
On the first iteration all vertices receive the
on subsequent iterations if a vertex does not receive a message
then the vertex-program is not invoked.
This function iterates until there are no remaining messages, or
graph- the input graph.
initialMsg- the message each vertex will receive at the first iteration
maxIterations- the maximum number of iterations to run for
activeDirection- the direction of edges incident to a vertex that received a message in the previous round on which to run
sendMsg. For example, if this is
EdgeDirection.Out, only out-edges of vertices that received a message in the previous round will run. The default is
EdgeDirection.Either, which will run
sendMsgon edges where either side received a message in the previous round. If this is
sendMsgwill only run on edges where *both* vertices received a message.
vprog- the user-defined vertex program which runs on each vertex and receives the inbound message and computes a new vertex value. On the first iteration the vertex program is invoked on all vertices and is passed the default message. On subsequent iterations the vertex program is only invoked on those vertices that receive messages.
sendMsg- a user supplied function that is applied to out edges of vertices that received messages in the current iteration
mergeMsg- a user supplied function that takes two incoming messages of type A and merges them into a single message of type A. ''This function must be commutative and associative and ideally the size of A should not increase.''