old_contents: import datetime
  
  from statscache_plugins.volume.utils import VolumePluginMixin, plugin_factory
  
  
  class PluginMixin(VolumePluginMixin):
      name = "volume"
      summary = "the number of messages coming across the bus"
      description = """
      This is perhaps the most simple metric catalogued by statscache.
      For any given time window, the number of messages are simply counted.
      It can give you a baseline quantity against which you could normalize
      other statistics.
      """
      _keys = ['timestamp']
  
      def process(self, message):
          timestamp = datetime.datetime.fromtimestamp(message['timestamp'])
          self._volumes[(timestamp,)] += 1
  
  
  plugins = plugin_factory(
      [datetime.timedelta(seconds=s) for s in [1, 5, 60]],
      PluginMixin,
      "Volume",
      "data_volume_",
      {
          'volume': sa.Column(sa.Integer, nullable=False),
      }
  )
  
new_contents: import datetime
  
  from statscache_plugins.volume.utils import VolumePluginMixin, plugin_factory
  
  import sqlalchemy as sa
  
  
  class PluginMixin(VolumePluginMixin):
      name = "volume"
      summary = "the number of messages coming across the bus"
      description = """
      This is perhaps the most simple metric catalogued by statscache.
      For any given time window, the number of messages are simply counted.
      It can give you a baseline quantity against which you could normalize
      other statistics.
      """
      _keys = ['timestamp']
  
      def process(self, message):
          timestamp = datetime.datetime.fromtimestamp(message['timestamp'])
          self._volumes[(timestamp,)] += 1
  
  
  plugins = plugin_factory(
      [datetime.timedelta(seconds=s) for s in [1, 5, 60]],
      PluginMixin,
      "Volume",
      "data_volume_",
      {
          'volume': sa.Column(sa.Integer, nullable=False),
      }
  )
  
subject: Add missing import