Function spawn_buffered 

pub fn spawn_buffered(
    input: Pin<Box<dyn RecordBatchStream<Item = Result<RecordBatch, DataFusionError>> + Send>>,
    buffer: usize,
) -> Pin<Box<dyn RecordBatchStream<Item = Result<RecordBatch, DataFusionError>> + Send>>

If running in a tokio context spawns the execution of stream to a separate task allowing it to execute in parallel with an intermediate buffer of size buffer