The Parquet scanner always transfers decompression buffers to the scratch batch:
These in turn are passed along with the row batch. This is safe but unnecessary in many cases where the batch does not hold pointers into the decompression buffer: if the column has only fixed-length data, or if the data page is dictionary-encoded.
This can make problems like
IMPALA-4923 worse than they would be otherwise because extra data is transferred across threads.