Feature Request: Optimization for large models about optimizer HOT 9 CLOSED

Connected to pydev debugger (build 213.7172.26)
[convert_sklearn] parse_sklearn_model
[convert_sklearn] convert_topology
[convert_operators] begin
[convert_operators] iteration 1 - n_vars=0 n_ops=3
[call_converter] call converter for 'SklearnScaler'.
[call_converter] call converter for 'SklearnRandomForestClassifier'.
[call_converter] call converter for 'SklearnZipMap'.
[convert_operators] end iter: 1 - n_vars=6
[convert_operators] iteration 2 - n_vars=6 n_ops=3
[convert_operators] end iter: 2 - n_vars=6
[convert_operators] end.
[_update_domain_version] +opset 0: name='', version=9
[_update_domain_version] +opset 1: name='ai.onnx.ml', version=1
[convert_sklearn] end

Process finished with exit code 1

Traceback (most recent call last):
  File "C:\Program Files\JetBrains\PyCharm 2021.3\plugins\python\helpers\pydev\pydevd.py", line 1483, in _exec
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File "C:\Program Files\JetBrains\PyCharm 2021.3\plugins\python\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:/Workspace/OnnxTest/pklconversion.py", line 126, in <module>
    onnx.save(onx, "bonus_model.onnx", save_as_external_data=True)
  File "C:\Users\....\AppData\Local\Programs\Python\Python37\lib\site-packages\onnx\__init__.py", line 202, in save_model
    s = _serialize(proto)
  File "C:\Users\....\AppData\Local\Programs\Python\Python37\lib\site-packages\onnx\__init__.py", line 71, in _serialize
    result = proto.SerializeToString()
ValueError: Message onnx.ModelProto exceeds maximum protobuf size of 2GB: 3354372734