How to save pynndescent index(0.1billion 128d)

[jiajieyao]

codes = np.fromfile(codes, f'<{dim}f4')
index = pynndescent.NNDescent(codes)
index.prepare()
with open(os.path.join(dest_dir, 'index'), 'wb') as fw:
pickle.dump(index, fw, protocol=4)

pickle big index occurs error? pynndescent has write index interface?