docs: public static void mergeTrackers(Map<Integer, Map<Integer, DRSiteDrIdTracker>> base,
                                       Map<Integer, Map<Integer, DRSiteDrIdTracker>> add)
      {
          for (Map.Entry<Integer, Map<Integer, DRSiteDrIdTracker>> clusterEntry : add.entrySet()) {
              final Map<Integer, DRSiteDrIdTracker> baseClusterEntry = base.get(clusterEntry.getKey());
              if (baseClusterEntry == null) {
                  base.put(clusterEntry.getKey(), clusterEntry.getValue());
              } else {
                  for (Map.Entry<Integer, DRSiteDrIdTracker> partitionEntry : clusterEntry.getValue().entrySet()) {
                      final DRConsumerDrIdTracker basePartitionTracker = baseClusterEntry.get(partitionEntry.getKey());
                      if (basePartitionTracker == null) {
                          baseClusterEntry.put(partitionEntry.getKey(), partitionEntry.getValue());
                      } else {
                          basePartitionTracker.mergeTracker(partitionEntry.getValue());
                      }
                  }
              }
          }
      }