flight_data_from_arrow_batch sends too much data

[asfimport]

Arrow arrays can share the same backing store, even if the array is just a "view" of a slice of another array.

Yet, when flight_data_from_arrow_batch encodes the arrays into a FlightData, it blindly copies the entire buffer ready to be sent over the wire.

Thus, for example, when DataFusion uses the arrow::compute::limit operator to return a few elements of an array, we still end up with a the full (potentially) large array being sent over the wire.

 

Since encoding the array in a FlightData involves copying the data anyway, perhaps it would be beneficial to take the Array length in consideration and copy only the parts of the buffer that contain actual data.

Reporter: Marko Mikulicic

_{Note: This issue was originally created as ARROW-12265. Please see the migration documentation for further details.}

[asfimport]

Andrew Lamb / @alamb:
Migrated to github: apache/arrow-rs#208