private void addQueueDoneSentinel() {
    // Add sentinel at the end of queue
    for (int i = 0; i < numLoadThreads; i++) {
      // add sentinel to the Queue not the batch!
      loadBatchQueues[i].add(elementBatches[i]);
      loadBatchQueues[i].add(DONE_SENTINEL);
    }
  }
HashTableLoader for Tez constructs the hashtable from records read from
a broadcast edge.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/mapjoin/fast/VectorMapJoinFastHashTableLoader.java