Why downloading sources of pyarrow and its requirements takes several minutes?

[Valentyn Tymofieiev]

Hi Arrow dev community,

Do you have any insight why

          python -m pip download --dest /tmp pyarrow==0.16.0 --no-binary
:all:

takes several minutes to execute? From the output we can see that pip get
stuck on:

  File was already downloaded /tmp/pyarrow-0.16.0.tar.gz
  Installing build dependencies ... |

There is a significant increase in runtime between 0.15.1 and 0.16.0. I
suspect  some build dependencies need to be installed before pip
understands the dependencies of pyarrow.  Is there some inefficiency in
Avro's setup.py that is causing this?

Thanks,
Valentyn