public long bulkSize() {
        long bulk = 0L;
        for (final Traverser.Admin<S> traverser : this.map.values()) {
            bulk = bulk + traverser.bulk();
        }
        return bulk;
    }
@author Marko A. Rodriguez (http://markorodriguez.com)
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/traverser/util/TraverserSet.java