void updateMaxIndex(int index) {
            if (index > logicalNodeCount) {
                upNodes.set(logicalNodeCount, index);
                logicalNodeCount = index;
            }
        }
Maintains a bitset where all non-down nodes have a bit set. All nodes that differ from defaultUp
and defaultDown are stored explicitly in a hash map.
vdslib/src/main/java/com/yahoo/vdslib/state/ClusterState.java