pymongo.errors.CursorNotFound: cursor id '…' not found at server

Question

I am trying to read about 1M documents from mongodb to csv file using pymongo. My code looks like:

import csv
from pymongo import MongoClient
from datetime import datetime
from bson import json_util
from tempfile import NamedTemporaryFile

client = MongoClient('mongodb://login:pass@server:port')
db = client.some_mongo_database
collection = db.some_mongo_collection

fromDate = datetime.strptime("2018-05-15 21:00", '%Y-%m-%d %H:%M')
tillDate = datetime.strptime("2018-05-16 21:00", '%Y-%m-%d %H:%M')
query = {
        "$or": [
                 {"LastUpdated": {"$gte": fromDate
                                , "$lt": tillDate}
                 },
                 {"$and": [
                            {"Created": {"$gte": fromDate
                                       , "$lt": tillDate}
                            },
                            {"LastUpdated": None}
                       ]
                  }
            ]
        }

cursor = collection.find(query, no_cursor_timeout=True)

after that if I'l do:

for row in cursor:
    print(row)
cursor.close()

everything works fine, and I could get all the documents. But if I do something like that:

with NamedTemporaryFile("w", delete=False) as temp:
    csv_writer = csv.writer(temp, delimiter='\t', quotechar='\b', quoting=csv.QUOTE_MINIMAL)
    for row in cursor:
        csv_row = [ [[row['_id']], str(json.dumps(row,default=json_util.default))] ]
        csv_writer.writerows(csv_row)
cursor.close()

After about 2 minutes and 200k documents I'm receive:

Traceback (most recent call last):
  File "mongo_data_loader.py", line 25, in <module>
    for row in cursor:

  File "/Library/Python/2.7/site-packages/pymongo/cursor.py", line 1169, in next
    if len(self.__data) or self._refresh():
  File "/Library/Python/2.7/site-packages/pymongo/cursor.py", line 1106, in _refresh
    self.__send_message(g)
  File "/Library/Python/2.7/site-packages/pymongo/cursor.py", line 975, in __send_message
    helpers._check_command_response(first)
  File "/Library/Python/2.7/site-packages/pymongo/helpers.py", line 142, in _check_command_response
    raise CursorNotFound(errmsg, code, response)
pymongo.errors.CursorNotFound: cursor id 184972541202 not found

What am I doing wrong?

Python 2.7.10
pymongo 3.6.1
mongo db.version() 3.6.5

Answer 1

As a temporary workaround I've made:

processed = 0

while True:
    cursor = collection.find(query, no_cursor_timeout=True).skip(processed)

    try:
        for row in cursor:
            csv_row = [ [[row['_id']], str(json.dumps(row,default=json_util.default))] ]
            csv_writer.writerows(csv_row)
            processed += 1
        cursor.close()
        break
    except CursorNotFound:
        print("Lost cursor. Retry with skip")

But the question about behavior described above is still actual