code: def _is_at_materialization_boundary(pcollection):
      """Determines whether a PCollection is at a materialization boundary."""
      # Ascend the hierarchy of composite PTransforms. In the Beam pipeline
      # graph, each AppliedPTransform has its "composite parent" stored in its
      # .parent field. Here, we check to see whether, at any of the composite
      # levels, the transform is a materialization boundary.
      current = pcollection.producer
      while current:
          if (
              current.transform
              and current.transform.__class__
              in _MATERIALIZATION_BARRIER_TRANSFORMS
          ):
              return True
          if pcollection in current.parent.outputs.values():
              current = current.parent
          else:
              break
      return False
  
file_path: transform/tensorflow_transform/beam/deep_copy.py
imports: import queue
  import apache_beam
  from apache_beam import pipeline
  from apache_beam import pvalue
  from apache_beam.pvalue import PCollection
  from apache_beam.transforms import resources
label_desc: Use image node_id 1 for calling a global function with example usage: _is_at_materialization_boundary(pcollection) and returns: False, True