private static boolean equalsWithDescription(NodeState a, NodeState b) {
            // This is due to NodeState.equals considers semantic equality, and description is not part of that.
            return a.equals(b) && ((a.getState() != State.DOWN) || a.getDescription().equals(b.getDescription()));
        }
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