I ran a python3.5 to etl from mongo into postgresql with pymongo and psycopg2.

When cursor is ready for loop
This error happend

Before 11200 items data have been etl success.

for u in items:

File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/pymongo/cursor.py", line 1097, in next
if len(self.__data) or self._refresh():
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/pymongo/cursor.py", line 1019, in _refresh
self.__read_concern))
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/pymongo/cursor.py", line 903, in __send_message
codec_options=self.__codec_options)
File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages/pymongo/helpers.py", line 128, in _unpack_response
error_object)
pymongo.errors.OperationFailure: database error: Runner error: Overflow sort stage buffered data usage of 33556536 bytes exceeds internal limit of 33554432 bytes