title: InterfaceError: connection already closed (using django + celery + Scrapy)
body: <p>I am getting this when using a Scrapy parsing function (that can take till 10 minutes sometimes) inside a Celery task.</p>
  
  <p>I use:
  - Django==1.6.5
  - django-celery==3.1.16
  - celery==3.1.16
  - psycopg2==2.5.5 (I used also psycopg2==2.5.4)</p>
  
  <pre>
  [2015-07-19 11:27:49,488: CRITICAL/MainProcess] Task myapp.parse_items[63fc40eb-c0d6-46f4-a64e-acce8301d29a] INTERNAL ERROR: InterfaceError('connection already closed',)
  Traceback (most recent call last):
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/celery/app/trace.py", line 284, in trace_task
      uuid, retval, SUCCESS, request=task_request,
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/celery/backends/base.py", line 248, in store_result
      request=request, **kwargs)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/djcelery/backends/database.py", line 29, in _store_result
      traceback=traceback, children=self.current_task_children(request),
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/djcelery/managers.py", line 42, in _inner
      return fun(*args, **kwargs)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/djcelery/managers.py", line 181, in store_result
      'meta': {'children': children}})
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/djcelery/managers.py", line 87, in update_or_create
      return get_queryset(self).update_or_create(**kwargs)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/djcelery/managers.py", line 70, in update_or_create
      obj, created = self.get_or_create(**kwargs)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/query.py", line 376, in get_or_create
      return self.get(**lookup), False
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/query.py", line 304, in get
      num = len(clone)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/query.py", line 77, in __len__
      self._fetch_all()
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/query.py", line 857, in _fetch_all
      self._result_cache = list(self.iterator())
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/query.py", line 220, in iterator
      for row in compiler.results_iter():
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 713, in results_iter
      for rows in self.execute_sql(MULTI):
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 785, in execute_sql
      cursor = self.connection.cursor()
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/backends/__init__.py", line 160, in cursor
      cursor = self.make_debug_cursor(self._cursor())
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/backends/__init__.py", line 134, in _cursor
      return self.create_cursor()
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/utils.py", line 99, in __exit__
      six.reraise(dj_exc_type, dj_exc_value, traceback)
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/backends/__init__.py", line 134, in _cursor
      return self.create_cursor()
    File "/home/mo/Work/python/pb-env/local/lib/python2.7/site-packages/django/db/backends/postgresql_psycopg2/base.py", line 137, in create_cursor
      cursor = self.connection.cursor()
  InterfaceError: connection already closed
  </pre>