@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);
}
@Override
public void cleanup(Context context) throws IOException, InterruptedException {
// Now emit the messages all at once.
IntWritable k = new IntWritable();
PageRankNode mass = new PageRankNode();
for (MapIF.Entry e : map.entrySet()) {
k.set(e.getKey());
mass.setNodeId(e.getKey());
mass.setType(PageRankNode.Type.Mass);
mass.setPageRank(e.getValue());
context.write(k, mass);
}
}
