@Override
  public void process(Object row, int tag) throws HiveException {

    VectorizedRowBatch batch = (VectorizedRowBatch) row;
    alias = (byte) tag;

    if (needCommonSetup) {

      // Our one time process method initialization.
      commonSetup();

      needCommonSetup = false;
    }

    if (needFirstBatchSetup) {

      // Our one time first-batch method initialization.
      firstBatchSetup(batch);

      needFirstBatchSetup = false;
    }

    if (needHashTableSetup) {

      // Setup our hash table specialization.  It will be the first time the process
      // method is called, or after a Hybrid Grace reload.

      hashTableSetup();

      needHashTableSetup = false;
    }

    batchCounter++;

    if (batch.size == 0) {
      return;
    }

    rowCounter += batch.size;

    processBatch(batch);
  }
This override lets us substitute our own fast vectorized hash table loader.
ql/src/java/org/apache/hadoop/hive/ql/exec/vector/mapjoin/VectorMapJoinCommonOperator.java