Cannot save big Frame

[st-pasha]

If a Frame contains any column over 2GB in size, the frame will fail to save. This appears to be caused by the limitations of standard library's write(), which is unable to write more than 2GB of data.

import datatable as dt
frame0 = dt.Frame(A=[1.0, 2.0, 10.0])
frame0.nrows = 2**28  # 8 bytes per row
frame0.save("test.jay", format="jay")

produces

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/pasha/py36/lib/python3.6/site-packages/typesentry/config.py", line 155, in fdecorated
    ret = f(*args, **kws)
  File "/Users/pasha/github/datatable/datatable/nff.py", line 48, in save
    self.internal.save_jay(dest, self.names, _strategy)
RuntimeError: Cannot write to file: [errno 22] Invalid argument (bytes already written: 8)