Block report statistics.
   * 
   * Each thread here represents its own data-node.
   * Data-nodes send the same block report each time.
   * The block report may contain missing or non-existing blocks.
Block report statistics.
   * 
   * Each thread here represents its own data-node.
   * Data-nodes send the same block report each time.
   * The block report may contain missing or non-existing blocks. | NNThroughputBenchmark.java