Big documents are not stored in the mongo db
```
3|datasets-preview-backend-worker  | DEBUG: 2021-10-27 07:08:33,384 - worker - job finished: 6178fae6d6a08142f3961667 for dataset: the_pile_books3
3|datasets-preview-backend-worker  | Traceback (most recent call last):
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 97, in <module>
3|datasets-preview-backend-worker  |     loop()
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 89, in loop
3|datasets-preview-backend-worker  |     process_next_job()
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 46, in process_next_job
3|datasets-preview-backend-worker  |     upsert_dataset_cache(dataset_name, "valid", dataset)
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 66, in upsert_dataset_cache
3|datasets-preview-backend-worker  |     DatasetCache(dataset_name=dataset_name, status=status, content=content).save()
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 407, in save
3|datasets-preview-backend-worker  |     object_id = self._save_create(doc, force_insert, write_concern)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 468, in _save_create
3|datasets-preview-backend-worker  |     raw_object = wc_collection.find_one_and_replace(select_dict, doc)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3167, in find_one_and_replace
3|datasets-preview-backend-worker  |     return self.__find_and_modify(filter, projection,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3017, in __find_and_modify
3|datasets-preview-backend-worker  |     return self.__database.client._retryable_write(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1552, in _retryable_write
3|datasets-preview-backend-worker  |     return self._retry_with_session(retryable, func, s, None)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1438, in _retry_with_session
3|datasets-preview-backend-worker  |     return self._retry_internal(retryable, func, session, bulk)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1470, in _retry_internal
3|datasets-preview-backend-worker  |     return func(session, sock_info, retryable)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3007, in _find_and_modify
3|datasets-preview-backend-worker  |     out = self._command(sock_info, cmd,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 238, in _command
3|datasets-preview-backend-worker  |     return sock_info.command(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/pool.py", line 726, in command
3|datasets-preview-backend-worker  |     self._raise_connection_failure(error)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/pool.py", line 710, in command
3|datasets-preview-backend-worker  |     return command(self, dbname, spec, secondary_ok,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/network.py", line 136, in command
3|datasets-preview-backend-worker  |     message._raise_document_too_large(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/message.py", line 1140, in _raise_document_too_large
3|datasets-preview-backend-worker  |     raise DocumentTooLarge("%r command document too large" % (operation,))
3|datasets-preview-backend-worker  | pymongo.errors.DocumentTooLarge: 'findAndModify' command document too large
```
Big documents are not stored in the mongo db: ```
3|datasets-preview-backend-worker  | DEBUG: 2021-10-27 07:08:33,384 - worker - job finished: 6178fae6d6a08142f3961667 for dataset: the_pile_books3
3|datasets-preview-backend-worker  | Traceback (most recent call last):
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 97, in <module>
3|datasets-preview-backend-worker  |     loop()
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 89, in loop
3|datasets-preview-backend-worker  |     process_next_job()
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/worker.py", line 46, in process_next_job
3|datasets-preview-backend-worker  |     upsert_dataset_cache(dataset_name, "valid", dataset)
3|datasets-preview-backend-worker  |   File "/home/hf/datasets-preview-backend/src/datasets_preview_backend/io/cache.py", line 66, in upsert_dataset_cache
3|datasets-preview-backend-worker  |     DatasetCache(dataset_name=dataset_name, status=status, content=content).save()
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 407, in save
3|datasets-preview-backend-worker  |     object_id = self._save_create(doc, force_insert, write_concern)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/mongoengine/document.py", line 468, in _save_create
3|datasets-preview-backend-worker  |     raw_object = wc_collection.find_one_and_replace(select_dict, doc)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3167, in find_one_and_replace
3|datasets-preview-backend-worker  |     return self.__find_and_modify(filter, projection,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3017, in __find_and_modify
3|datasets-preview-backend-worker  |     return self.__database.client._retryable_write(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1552, in _retryable_write
3|datasets-preview-backend-worker  |     return self._retry_with_session(retryable, func, s, None)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1438, in _retry_with_session
3|datasets-preview-backend-worker  |     return self._retry_internal(retryable, func, session, bulk)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/mongo_client.py", line 1470, in _retry_internal
3|datasets-preview-backend-worker  |     return func(session, sock_info, retryable)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 3007, in _find_and_modify
3|datasets-preview-backend-worker  |     out = self._command(sock_info, cmd,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/collection.py", line 238, in _command
3|datasets-preview-backend-worker  |     return sock_info.command(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/pool.py", line 726, in command
3|datasets-preview-backend-worker  |     self._raise_connection_failure(error)
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/pool.py", line 710, in command
3|datasets-preview-backend-worker  |     return command(self, dbname, spec, secondary_ok,
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/network.py", line 136, in command
3|datasets-preview-backend-worker  |     message._raise_document_too_large(
3|datasets-preview-backend-worker  |   File "/home/hf/.cache/pypoetry/virtualenvs/datasets-preview-backend-CTHb2hp_-py3.9/lib/python3.9/site-packages/pymongo/message.py", line 1140, in _raise_document_too_large
3|datasets-preview-backend-worker  |     raise DocumentTooLarge("%r command document too large" % (operation,))
3|datasets-preview-backend-worker  | pymongo.errors.DocumentTooLarge: 'findAndModify' command document too large
```