title: Django database cache TIMEOUT - make backend delete row
body: <p>I'm not sure what <code>Django</code> database cache does with expired entries but it seems that they remain in the database. </p>
  
  <p>I want <code>Django</code> to delete them after they expire because their size is huge and there can be unlimited number of different keys. </p>
  
  <pre><code>CACHES = {
      'default': {
          'BACKEND': 'django.core.cache.backends.db.DatabaseCache',
          'LOCATION': 'cache_table',
          'TIMEOUT': 60 * 20,
      }
  }
  </code></pre>
  
  <p>I use <code>cache</code> on filtered list of objects and this filter contais number and char fields.</p>
  
  <p>Is it possible?</p>