public void doRequest(ServerData<I, V, E, M> serverData) {
ConcurrentHashMap<I, VertexMutations<I, V, E, M>> vertexMutations =
serverData.getVertexMutations();
Histogram verticesInMutationHist = GiraphMetrics.get().perSuperstep()
.getUniformHistogram(MetricNames.VERTICES_IN_MUTATION_REQUEST);
verticesInMutationHist.update(vertexMutations.size());
for (Entry<I, VertexMutations<I, V, E, M>> entry :
vertexIdMutations.entrySet()) {
VertexMutations<I, V, E, M> mutations =
vertexMutations.get(entry.getKey());
if (mutations == null) {