@Override
  public long calculateMaxReturnSize() {
    long maxReturnSize = 0;
    for (Operator child : children) {
      maxReturnSize = Math.max(maxReturnSize, child.calculateMaxReturnSize());
    }
    return maxReturnSize;
  }
prepare next batch

@return true if need to break current loop, otherwise false
@throws Exception errors happened while fetching next batch data
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/last/LastQueryMergeOperator.java