long getPartitionSealedCount() {
      long count = 0;
      for (AmbryPartition partition : partitionMap.values()) {
        if (partition.getPartitionState() == PartitionState.READ_ONLY) {
          count++;
        }
      }
      return count;
    }
@return the count of partitions that are in sealed (read-only) state.
ambry-clustermap/src/main/java/com/github/ambry/clustermap/HelixClusterManager.java