@Override
  public long ramBytesUsed() {
    return INSTANCE_SIZE
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(sourceId)
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(operatorContext)
        + MemoryEstimationHelper.getEstimatedSizeOfAccountableObject(sourceHandle);
  }
For ExchangeOperator in pipeline, the maxReturnSize is equal to the maxReturnSize of the child
operator.

@param maxReturnSize max return size of child operator
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/operator/source/ExchangeOperator.java