title: relation "django_session" does not exist
body: <p>Now I am new in heroku and trying to deploy my django app on heroku. It was successful by just following instructions and I could test in heroku. 
  But after I changed my local db from sqlite to postgres, I can not go further because of the error. It might be related to DB. My app is still working good in local base but not in heroku while I push all to heroku.</p>
  
  <p>base.py</p>
  
  <pre><code>DATABASES = {
      'default': {
          'ENGINE': 'django.db.backends.postgresql_psycopg2',
          'NAME': 'postgres',
          'USER': 'postgres',
          'PASSWORD': '',
          'HOST': '',
          'PORT': '',
      }
  }
  db_from_env = dj_database_url.config()
  DATABASES['default'].update(db_from_env)
  </code></pre>
  
  <p>error message on debug mode</p>
  
  <pre><code>ProgrammingError at /
  relation "django_session" does not exist
  LINE 1: ...ession_data", "django_session"."expire_date" FROM "django_se...
                                                               ^
  Request Method: GET
  Request URL:    https://happybom.herokuapp.com/
  Django Version: 2.0.4
  Exception Type: ProgrammingError
  Exception Value:    
  relation "django_session" does not exist
  LINE 1: ...ession_data", "django_session"."expire_date" FROM "django_se...
                                                               ^
  Exception Location: /app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py in _execute, line 85
  Python Executable:  /app/.heroku/python/bin/python
  Python Version: 3.6.4
  Python Path:    
  ['/app/.heroku/python/bin',
   '/app',
   '/app/.heroku/python/lib/python36.zip',
   '/app/.heroku/python/lib/python3.6',
   '/app/.heroku/python/lib/python3.6/lib-dynload',
   '/app/.heroku/python/lib/python3.6/site-packages']
  </code></pre>
  
  <p>heroku logs</p>
  
  <pre><code>2018-06-27T16:19:46.500148+00:00 app[api]: Starting process with command `bash` by user txxx@gmail.com
  2018-06-27T16:19:54.976946+00:00 heroku[run.8196]: Awaiting client
  2018-06-27T16:19:55.035413+00:00 heroku[run.8196]: Starting process with command `bash`
  2018-06-27T16:19:55.078847+00:00 heroku[run.8196]: State changed from starting to up
  2018-06-27T16:20:17.457935+00:00 heroku[run.8196]: Client connection closed. Sending SIGHUP to all processes
  2018-06-27T16:20:17.995204+00:00 heroku[run.8196]: Process exited with status 129
  2018-06-27T16:20:18.015161+00:00 heroku[run.8196]: State changed from up to complete
  2018-06-27T16:21:37.988762+00:00 app[api]: Starting process with command `bash` by user txxx@gmail.com
  2018-06-27T16:21:49.979009+00:00 heroku[run.2682]: Awaiting client
  2018-06-27T16:21:50.038333+00:00 heroku[run.2682]: Starting process with command `bash`
  2018-06-27T16:21:50.171144+00:00 heroku[run.2682]: State changed from starting to up
  2018-06-27T16:52:53.428934+00:00 heroku[run.2682]: Client connection closed. Sending SIGHUP to all processes
  2018-06-27T16:52:53.967773+00:00 heroku[run.2682]: Process exited with status 129
  2018-06-27T16:52:54.005827+00:00 heroku[run.2682]: State changed from up to complete
  2018-06-27T17:02:52.720107+00:00 heroku[web.1]: Unidling
  2018-06-27T17:02:52.720404+00:00 heroku[web.1]: State changed from down to starting
  2018-06-27T17:02:57.851621+00:00 heroku[web.1]: Starting process with command `gunicorn estimate.wsgi`
  2018-06-27T17:03:00.563084+00:00 app[web.1]: [2018-06-27 17:03:00 +0000] [4] [INFO] Starting gunicorn 19.8.0
  2018-06-27T17:03:00.563690+00:00 app[web.1]: [2018-06-27 17:03:00 +0000] [4] [INFO] Listening at: http://0.0.0.0:35753 (4)
  2018-06-27T17:03:00.567579+00:00 app[web.1]: [2018-06-27 17:03:00 +0000] [8] [INFO] Booting worker with pid: 8
  2018-06-27T17:03:00.563791+00:00 app[web.1]: [2018-06-27 17:03:00 +0000] [4] [INFO] Using worker: sync
  2018-06-27T17:03:00.587739+00:00 app[web.1]: [2018-06-27 17:03:00 +0000] [9] [INFO] Booting worker with pid: 9
  2018-06-27T17:03:02.002190+00:00 heroku[web.1]: State changed from starting to up
  2018-06-27T17:03:02.895543+00:00 app[web.1]: Internal Server Error: /
  2018-06-27T17:03:02.895572+00:00 app[web.1]: Traceback (most recent call last):
  2018-06-27T17:03:02.895573+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/contrib/sessions/backends/base.py", line 191, in _get_session
  2018-06-27T17:03:02.895575+00:00 app[web.1]: return self._session_cache
  2018-06-27T17:03:02.895576+00:00 app[web.1]: AttributeError: 'SessionStore' object has no attribute '_session_cache'
  2018-06-27T17:03:02.895578+00:00 app[web.1]:
  2018-06-27T17:03:02.895580+00:00 app[web.1]:
  2018-06-27T17:03:02.895579+00:00 app[web.1]: During handling of the above exception, another exception occurred:
  2018-06-27T17:03:02.895582+00:00 app[web.1]: Traceback (most recent call last):
  2018-06-27T17:03:02.895583+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/django/db/backends/utils.py", line 85, in _execute
  2018-06-27T17:03:02.895584+00:00 app[web.1]: return self.cursor.execute(sql, params)
  2018-06-27T17:03:02.895585+00:00 app[web.1]: psycopg2.ProgrammingError: relation "django_session" does not exist
  2018-06-27T17:03:02.895586+00:00 app[web.1]: LINE 1: ...ession_data", "django_session"."expire_date" FROM "django_se...
  2018-06-27T17:03:02.895588+00:00 app[web.1]: ^
  2018-06-27T17:03:02.895589+00:00 app[web.1]:
  2018-06-27T17:03:02.895590+00:00 app[web.1]:
  2018-06-27T17:03:02.895591+00:00 app[web.1]: The above exception was the direct cause of the following exception:
  </code></pre>
  
  <p>heroku db status</p>
  
  <p>heroku pg:info</p>
  
  <pre><code>=== HEROKU_POSTGRESQL_COPPER_URL, DATABASE_URL
  Plan:                  Hobby-dev
  Status:                Available
  Connections:           0/20
  PG Version:            10.4
  Created:               2018-06-26 03:07 UTC
  Data Size:             7.6 MB
  Tables:                0
  Rows:                  0/10000 (In compliance)
  Fork/Follow:           Unsupported
  Rollback:              Unsupported
  Continuous Protection: Off
  Add-on:                postgresql-globular-10516
  
  === HEROKU_POSTGRESQL_CHARCOAL_URL
  Plan:                  Hobby-dev
  Status:                Available
  Connections:           0/20
  PG Version:            10.4
  Created:               2018-04-28 23:05 UTC
  Data Size:             7.9 MB
  Tables:                0
  Rows:                  0/10000 (In compliance)
  Fork/Follow:           Unsupported
  Rollback:              Unsupported
  Continuous Protection: Off
  Add-on:                postgresql-shaped-32846
  </code></pre>
  
  <p>heroku pg:diagnose --app happybom</p>
  
  <pre><code>Report 4264cbec-925d-40d3-ad75-45bee458d28e for happybom::DATABASE_URL
  available for one month after creation on 2018-06-27T17:38:29.568775+00:00
  
  GREEN: Connection Count
  GREEN: Long Queries
  GREEN: Idle in Transaction
  GREEN: Indexes
  GREEN: Bloat
  GREEN: Hit Rate
  GREEN: Blocking Queries
  GREEN: Sequences
  SKIPPED: Load
  Error Load check not supported on this plan
  </code></pre>