MongoDB find operation throws OperationFailure: Cannot update value

Recently have started facing this issue where we are unable to read a chunk of data from AWS DocumentDB. To set the context, our read looks something like this.

batch_data = self._db.find({"key_one": self._value1, "key_two": self._value2}, self._projector).sort("_id", 1).skip(offset).limit(batch_size)
for document in batch_data:
    # some code

The keys that I’m storing with are indexed. While this perfectly works with some environments, this isn’t working in production and fails intermittently with the below stack trace.

Traceback (most recent call last):
 for document in batch_data:
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 1156, in next
    if len(self.__data) or self._refresh():
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 1073, in _refresh
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 953, in __send_message
    response = client._run_operation_with_response(
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 1342, in _run_operation_with_response
    return self._retryable_read(
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 1464, in _retryable_read
    return func(session, server, sock_info, slave_ok)
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 1334, in _cmd
    return server.run_operation_with_response(
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 136, in run_operation_with_response
  File "/usr/local/lib/python3.8/site-packages/pymongo/", line 159, in _check_command_response
    raise OperationFailure(msg % errmsg, code, response)
    pymongo.errors.OperationFailure: Cannot update value", "filename": ""}

The exception occurs in this line where we are trying to loop through our cursor to process individual records.

for document in batch_data: # Error in this line

Also to note that that we aren’t trying an update or an upsert action here. We are plainly trying to read data in batches. There’s only one stackoverflow issue which relates to our stack trace here.

This has started occurring only since last week and we’re unable to find more resources on the internet to fix this issue. Can anyone help us what is going wrong here?

Hi @Sameera_Sy,
Can you please show the relevant lines in the mongod log file?

@Rafael_Green I will share the logs by tomorrow.

Welcome to the MongoDB Community Forums @Sameera_Sy!

I can’t find the referenced error message in the MongoDB server or Python driver code so it looks like the issue you are encountering may be specific to DocumentDB’s emulated MongoDB interface (similar to the question you referenced on Stack Overflow).

AWS DocumentDB is an independent implementation of a subset of genuine MongoDB server features, so this problem would be best addressed by AWS support or with a broader audience like Stack Overflow.

You could try testing the same code against a MongoDB Atlas cluster on AWS (there’s a free tier), however that won’t provide any assurance that DocumentDB will have a consistent outcome.