Package org.neo4j.graphalgo.beta.pregel

Interface PregelComputation<C extends PregelConfig>

  • public interface PregelComputation<C extends PregelConfig>
    Main interface to express user-defined logic using the Pregel framework. An algorithm is expressed using a node-centric view. A node can receive messages from other nodes, change its state and send messages to other nodes in each iteration (superstep).
    See Also:
    Pregel, Paper

    • Method Summary

      All Methods Instance Methods Abstract Methods Default Methods 
      Modifier and Type Method Description
      default double applyRelationshipWeight​(double nodeValue, double relationshipWeight)
      If the input graph is weighted, i.e.
      void compute​(ComputeContext<C> context, Messages messages)
      The compute method is called individually for each node in every superstep as long as the node receives messages or has not voted to halt yet.
      default void init​(InitContext<C> context)
      The init method is called in the beginning of the first superstep (iteration) of the Pregel computation and allows initializing node values.
      default void masterCompute​(MasterComputeContext<C> context)
      The masterCompute method is called exactly once after every superstep.
      default java.util.Optional<Reducer> reducer()
      A reducer is used to combine messages sent to a single node.
      PregelSchema schema​(C config)
      The schema describes the node property layout.

    • Method Detail

      • schema

        PregelSchema schema​(C config)
        The schema describes the node property layout. A node property can be composed of multiple primitive values, such as double or long, as well as arrays of those. Each part of that composite schema is named by a unique key.
        Example: 
         public PregelSchema schema(PregelConfig config) {
      return new PregelSchema.Builder()
          .add("key", ValueType.LONG)
          .add("privateKey", ValueType.LONG, Visibility.PRIVATE)
          .build();
 }
        See Also:
        PregelSchema

      • init

        default void init​(InitContext<C> context)
        The init method is called in the beginning of the first superstep (iteration) of the Pregel computation and allows initializing node values.
        The context parameter provides access to node properties of the in-memory graph and the algorithm configuration.

      • compute

        void compute​(ComputeContext<C> context,
             Messages messages)
        The compute method is called individually for each node in every superstep as long as the node receives messages or has not voted to halt yet.
        Since a Pregel computation is state-less, a node can only communicate with other nodes via messages. In each super- step, a node receives messages via the input parameter and can send new messages via the context parameter. Messages can be sent to neighbor nodes or any node if the identifier is known.

      • masterCompute

        default void masterCompute​(MasterComputeContext<C> context)
        The masterCompute method is called exactly once after every superstep. It is called by a single thread.

      • reducer

        default java.util.Optional<Reducer> reducer()
        A reducer is used to combine messages sent to a single node. Based on the reduce function, multiple messages are condensed into a single one. Use cases are computing the sum, count, minimum or maximum of messages. Specifying a reducer can significantly reduce memory consumption and runtime of the computation.

      • applyRelationshipWeight

        default double applyRelationshipWeight​(double nodeValue,
                                       double relationshipWeight)
        If the input graph is weighted, i.e. relationships have a property, this method can be overridden to apply that weight on a message before it is read by the receiving node.
        If the input graph has no relationship properties, i.e. is unweighted, the method is skipped.