@Override
  public long calculateMaxReturnSize() {
    return children.stream().mapToLong(Operator::calculateMaxReturnSize).sum();
  }
Start index for each input TsBlocks and size of it is equal to inputTsBlocks.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/join/HorizontallyConcatOperator.java