我已经完全部署了django应用程序（debug=true），当我以某种方式查询数据库时，常常会丢失mysql连接并出现以下错误： Exception Value: (2013, 'Lost connection to MySQL server during query') . 这似乎是随机发生的。我可以进行5-8次查询，然后得到错误。发生这种情况的原因是什么？谢谢。
以下是完整的回溯：

Environment:

Request Method: GET
Request URL: https://www.tcgfirst.com/

Django Version: 2.0
Python Version: 3.6.6
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'whitenoise.runserver_nostatic',
 'django.contrib.staticfiles',
 'engine',
 'contact',
 'crispy_forms',
 'django.contrib.sites',
 'allauth',
 'allauth.account',
 'allauth.socialaccount',
 'stripe',
 'checkout']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'whitenoise.middleware.WhiteNoiseMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']

Traceback:

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in _get_session
  191.             return self._session_cache

During handling of the above exception ('SessionStore' object has no attribute '_session_cache'), another exception occurred:

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute
  85.                 return self.cursor.execute(sql, params)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/mysql/base.py" in execute
  71.             return self.cursor.execute(query, args)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in execute
  250.             self.errorhandler(self, exc, value)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/connections.py" in defaulterrorhandler
  50.         raise errorvalue

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in execute
  247.             res = self._query(query)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in _query
  411.         rowcount = self._do_query(q)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in _do_query
  374.         db.query(q)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/connections.py" in query
  277.             _mysql.connection.query(self, query)

The above exception ((2013, 'Lost connection to MySQL server during query')) was the direct cause of the following exception:

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/exception.py" in inner
  35.             response = get_response(request)

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  128.                 response = self.process_exception_by_middleware(e, request)

File "/app/.heroku/python/lib/python3.6/site-packages/django/core/handlers/base.py" in _get_response
  126.                 response = wrapped_callback(request, *callback_args,**callback_kwargs)

File "/app/engine/views.py" in home
  23.     cart = Cart(request)

File "/app/engine/cart.py" in __init__
  35.         cart = self.session.get(settings.CART_SESSION_KEY)

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in get
  66.         return self._session.get(key, default)

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py" in _get_session
  196.                 self._session_cache = self.load()

File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/db.py" in load
  34.                 expire_date__gt=timezone.now()

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/manager.py" in manager_method
  82.                 return getattr(self.get_queryset(), name)(*args,**kwargs)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in get
  397.         num = len(clone)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in __len__
  254.         self._fetch_all()

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in _fetch_all
  1179.             self._result_cache = list(self._iterable_class(self))

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/query.py" in __iter__
  54.         results = compiler.execute_sql(chunked_fetch=self.chunked_fetch, chunk_size=self.chunk_size)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/models/sql/compiler.py" in execute_sql
  1063.             cursor.execute(sql, params)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in execute
  100.             return super().execute(sql, params)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in execute
  68.         return self._execute_with_wrappers(sql, params, many=False, executor=self._execute)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute_with_wrappers
  77.         return executor(sql, params, many, context)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute
  85.                 return self.cursor.execute(sql, params)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py" in __exit__
  89.                 raise dj_exc_value.with_traceback(traceback) from exc_value

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py" in _execute
  85.                 return self.cursor.execute(sql, params)

File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/mysql/base.py" in execute
  71.             return self.cursor.execute(query, args)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in execute
  250.             self.errorhandler(self, exc, value)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/connections.py" in defaulterrorhandler
  50.         raise errorvalue

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in execute
  247.             res = self._query(query)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in _query
  411.         rowcount = self._do_query(q)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/cursors.py" in _do_query
  374.         db.query(q)

File "/app/.heroku/python/lib/python3.6/site-packages/MySQLdb/connections.py" in query
  277.             _mysql.connection.query(self, query)

Exception Type: OperationalError at /
Exception Value: (2013, 'Lost connection to MySQL server during query')