@Override
  public long calculateRetainedSizeAfterCallingNext() {
    // we can safely ignore one line cached in IFill
    return child.calculateRetainedSizeAfterCallingNext();
  }
Used for previous and constant value fill.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/process/AbstractFillOperator.java