public void initialize(Iterable<Object> values, Object keyObject, byte tag) {
      this.passDownKey = null;
      this.values = values.iterator();
      this.tag = tag;
      this.keyObject = keyObject;
    }
Process input from tez LogicalInput and write output - for a map plan
Just pump the records through the query plan.
ql/src/java/org/apache/hadoop/hive/ql/exec/tez/ReduceRecordSource.java