Exemplo n.º 1
0
    @Override
    public void map(IntWritable nid, PageRankNode node, Context context)
        throws IOException, InterruptedException {
      // Pass along node structure.
      intermediateStructure.setNodeId(node.getNodeId());
      intermediateStructure.setType(PageRankNode.Type.Structure);
      intermediateStructure.setAdjacencyList(node.getAdjacenyList());

      context.write(nid, intermediateStructure);

      int massMessages = 0;
      int massMessagesSaved = 0;

      // Distribute PageRank mass to neighbors (along outgoing edges).
      if (node.getAdjacenyList().size() > 0) {
        // Each neighbor gets an equal share of PageRank mass.
        ArrayListOfIntsWritable list = node.getAdjacenyList();
        float mass = node.getPageRank() - (float) StrictMath.log(list.size());

        context.getCounter(PageRank.edges).increment(list.size());

        // Iterate over neighbors.
        for (int i = 0; i < list.size(); i++) {
          int neighbor = list.get(i);

          if (map.containsKey(neighbor)) {
            // Already message destined for that node; add PageRank mass contribution.
            massMessagesSaved++;
            map.put(neighbor, sumLogProbs(map.get(neighbor), mass));
          } else {
            // New destination node; add new entry in map.
            massMessages++;
            map.put(neighbor, mass);
          }
        }
      }

      // Bookkeeping.
      context.getCounter(PageRank.nodes).increment(1);
      context.getCounter(PageRank.massMessages).increment(massMessages);
      context.getCounter(PageRank.massMessagesSaved).increment(massMessagesSaved);
    }
Exemplo n.º 2
0
    @Override
    public void map(IntWritable nid, PageRankNode node, Context context)
        throws IOException, InterruptedException {
      // Pass along node structure.
      intermediateStructure.setNodeId(node.getNodeId());
      intermediateStructure.setType(PageRankNode.Type.Structure);
      intermediateStructure.setAdjacencyList(node.getAdjacenyList());

      context.write(nid, intermediateStructure);

      int massMessages = 0;

      // Distribute PageRank mass to neighbors (along outgoing edges).
      if (node.getAdjacenyList().size() > 0) {
        // Each neighbor gets an equal share of PageRank mass.
        ArrayListOfIntsWritable list = node.getAdjacenyList();
        float mass = node.getPageRank() - (float) StrictMath.log(list.size());

        context.getCounter(PageRank.edges).increment(list.size());

        // Iterate over neighbors.
        for (int i = 0; i < list.size(); i++) {
          neighbor.set(list.get(i));
          intermediateMass.setNodeId(list.get(i));
          intermediateMass.setType(PageRankNode.Type.Mass);
          intermediateMass.setPageRank(mass);

          // Emit messages with PageRank mass to neighbors.
          context.write(neighbor, intermediateMass);
          massMessages++;
        }
      }

      // Bookkeeping.
      context.getCounter(PageRank.nodes).increment(1);
      context.getCounter(PageRank.massMessages).increment(massMessages);
    }
Exemplo n.º 3
0
    @Override
    public void reduce(IntWritable nid, Iterable<PageRankNode> iterable, Context context)
        throws IOException, InterruptedException {
      Iterator<PageRankNode> values = iterable.iterator();

      // Create the node structure that we're going to assemble back together from shuffled pieces.
      PageRankNode node = new PageRankNode();

      node.setType(PageRankNode.Type.Complete);
      node.setNodeId(nid.get());

      int massMessagesReceived = 0;
      int structureReceived = 0;

      float mass = Float.NEGATIVE_INFINITY;
      while (values.hasNext()) {
        PageRankNode n = values.next();

        if (n.getType().equals(PageRankNode.Type.Structure)) {
          // This is the structure; update accordingly.
          ArrayListOfIntsWritable list = n.getAdjacenyList();
          structureReceived++;

          node.setAdjacencyList(list);
        } else {
          // This is a message that contains PageRank mass; accumulate.
          mass = sumLogProbs(mass, n.getPageRank());
          massMessagesReceived++;
        }
      }

      // Update the final accumulated PageRank mass.
      node.setPageRank(mass);
      context.getCounter(PageRank.massMessagesReceived).increment(massMessagesReceived);

      // Error checking.
      if (structureReceived == 1) {
        // Everything checks out, emit final node structure with updated PageRank value.
        context.write(nid, node);

        // Keep track of total PageRank mass.
        totalMass = sumLogProbs(totalMass, mass);
      } else if (structureReceived == 0) {
        // We get into this situation if there exists an edge pointing to a node which has no
        // corresponding node structure (i.e., PageRank mass was passed to a non-existent node)...
        // log and count but move on.
        context.getCounter(PageRank.missingStructure).increment(1);
        LOG.warn(
            "No structure received for nodeid: " + nid.get() + " mass: " + massMessagesReceived);
        // It's important to note that we don't add the PageRank mass to total... if PageRank mass
        // was sent to a non-existent node, it should simply vanish.
      } else {
        // This shouldn't happen!
        throw new RuntimeException(
            "Multiple structure received for nodeid: "
                + nid.get()
                + " mass: "
                + massMessagesReceived
                + " struct: "
                + structureReceived);
      }
    }