new_contents: import time
  import datetime
  
  from django.db import connection, models, ProgrammingError
  
  from ..job import Job
  
  class DatabaseBackend(object):
      TABLE = 'django_lightweight_queue'
  
      FIELDS = (
          models.AutoField(name='id', primary_key=True),
          models.CharField(name='queue', max_length=255),
          models.TextField(name='data'),
          models.DateTimeField(name='created'),
      )
  
      def __init__(self):
          qn = connection.ops.quote_name
  
          sql = []
          for x in self.FIELDS:
              sql.append(' '.join((
                  qn(x.name),
                  x.db_type(connection=connection),
                  'PRIMARY KEY' if x.primary_key else '',
              )))
  
          cursor = connection.cursor()
          cursor.execute('CREATE TABLE IF NOT EXISTS %s (\n%s\n);' % (
              qn(self.TABLE),
              ',\n'.join(sql),
          ))
  
          try:
              cursor.execute('CREATE INDEX %s ON %s (%s, %s)' % (
                  qn('%s_idx' % self.TABLE),
                  qn(self.TABLE),
                  qn('queue'),
                  qn('created'),
              ))
          except ProgrammingError:
              # "IF NOT EXISTS" is not portable, so we just fail to create it
              pass
  
          # Don't share connections across fork()
          connection.close()
  
      def enqueue(self, job, queue):
          cursor = connection.cursor()
          cursor.execute("""
              INSERT INTO %s (queue, data, created) VALUES (%%s, %%s, %%s)
          """ % connection.ops.quote_name(self.TABLE), (
              queue,
              job.to_json(),
              datetime.datetime.utcnow(),
          ))
  
      def dequeue(self, queue, timeout):
          cursor = connection.cursor()
          cursor.execute("""
              SELECT id, data FROM %s WHERE queue = %%s
              ORDER BY created ASC LIMIT 1
          """ % connection.ops.quote_name(self.TABLE), (queue,))
  
          try:
              id_, data = cursor.fetchall()[0]
          except (IndexError, ProgrammingError):
              time.sleep(timeout)
              return
  
          cursor.execute("""
              DELETE FROM %s WHERE id = %%s
          """ % connection.ops.quote_name(self.TABLE), (id_,))
  
          try:
              return Job.from_json(data)
          except TypeError:
              pass
  
subject: Add experimental polling DB backend.