private void prepareForTimeHeap() {
    for (int i = 0; i < inputOperatorsCount; i++) {
      if (inputIndex[i] != shadowInputIndex[i]) {
        inputIndex[i] = shadowInputIndex[i];
        if (!isEmpty(i)) {
          updateTimeSelector(i);
        }
      }
    }
  }
This field indicates each data type for output columns(not including time column) of
TimeJoinOperator its size should be equal to outputColumnCount.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/FullOuterTimeJoinOperator.java