@Override
  public void dumpMetrics() {
    for (int i = 0; i < hashPartitions.length; i++) {
      HashPartition hp = hashPartitions[i];
      if (hp.hashMap != null) {
        hp.hashMap.debugDumpMetrics();
      }
    }
  }
Sometimes, when container is empty in multi-table mapjoin, we need to add a dummy row.
This container does not normally support adding rows; this is for the dummy row.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/HybridHashTableContainer.java