[Question] How is batch_size auto tuned by beam in BeamSource

[zexuan-zhou]

Hi,

I'm reading https://www.tensorflow.org/tfx/tfx_bsl/api_docs/python/tfx_bsl/public/tfxio/TFXIO and I saw for BeamSource

@abc.abstractmethod
BeamSource(
    batch_size: Optional[int] = None
) -> beam.PTransform

It says

batch_size	if not None, the pa.RecordBatch produced will be of the specified size. Otherwise it's automatically tuned by Beam.

I wonder how beam auto tunes this variable. Could anyone provide any insight? Thanks a lot