@Override
  public boolean pushRecord() throws HiveException {
    execContext.resetRow();

    try {
      if (reader.next()) {
        Object value;
        try {
          value = reader.getCurrentValue();
        } catch (IOException e) {
          closeReader();
          throw new HiveException(e);
        }
        return processRow(value);
      } else if (flushLastRecord) {
        mapOp.flushRecursive();
      }
    } catch (IOException e) {
      closeReader();
      throw new HiveException(e);
    }
    return false;
  }
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/MapRecordSource.java