@Override
  public long calculateMaxPeekMemory() {
    // while doing constant and previous fill, we may need to copy the corresponding column if there
    // exists null values
    // so the max peek memory may be double
    return 2 * child.calculateMaxPeekMemory() + 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