@Override
        public boolean visitGroup(Group group) {
            if (group.isLeafGroup()) {
                if (safeMaintenanceGroupThreshold > 0 &&
                        computeNodesSafelySetToMaintenance(group) >= safeMaintenanceGroupThreshold) {
                    markAllAvailableGroupNodeIndicesAsMaintained(group);
                } else if (computeGroupAvailability(group) < minNodeRatioPerGroup) {
                    markAllAvailableGroupNodeIndicesAsDown(group);
                }
            }
            return true;
        }
If the number of nodes safely set to maintenance is at least this number, the remaining
nodes in the group will be set to maintenance (storage nodes) or down (distributors).

<p>This feature is disabled if safeMaintenanceGroupThreshold is 0 (not default).</p>
clustercontroller-core/src/main/java/com/yahoo/vespa/clustercontroller/core/GroupAvailabilityCalculator.java