title: why use django haystack slice queryset too slow?
body: <p>I use whoosh as the search backend.</p>
  
  <p>when I get just 3 search result, code:</p>
  
  <blockquote>
  <pre><code>#!/usr/bin/python
  # -*- coding: utf-8 -*-
  import sys
  sys.path.append('/home/guomeng/projects/tapplex_ringtones')
  import os
  os.environ['DJANGO_SETTINGS_MODULE'] = "tapplex_ringtones.settings"
  
  from haystack.query import SearchQuerySet
  from ringtones.models import Ringtone
  import time
  
  query_word = u'sky'
  t0 = time.time()
  sqs = SearchQuerySet().models(Ringtone).filter(content=query_word)[:3]
  t1 = time.time()
  print sqs
  print t1 - t0
  </code></pre>
  </blockquote>
  
  <p>the result is:</p>
  
  <pre><code>[&lt;SearchResult: ringtones.ringtone (pk=u'1730')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'28959')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'25889')&gt;]
  0.422543048859&gt; 0.422543048859
  </code></pre>
  
  <p>when I get all search result, code:</p>
  
  <blockquote>
  <pre><code>#!/usr/bin/python
  # -*- coding: utf-8 -*-
  import sys
  sys.path.append('/home/guomeng/projects/tapplex_ringtones')
  import os
  os.environ['DJANGO_SETTINGS_MODULE'] = "tapplex_ringtones.settings"
  
  from haystack.query import SearchQuerySet
  from ringtones.models import Ringtone
  import time
  
  query_word = u'sky'
  t0 = time.time()
  sqs = SearchQuerySet().models(Ringtone).filter(content=query_word)
  t1 = time.time()
  print sqs
  print t1 - t0
  </code></pre>
  </blockquote>
  
  <p>the result is:</p>
  
  <pre><code>[&lt;SearchResult: ringtones.ringtone (pk=u'1730')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'28959')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'25889')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'5303')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'5335')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'5411')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'1212')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'28473')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'23867')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'27087')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'26849')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'2973')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'2645')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'31007')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'11637')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'16957')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'106')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'2481')&gt;, &lt;SearchResult: ringtones.ringtone (pk=u'15697')&gt;]
  0.19460105896
  </code></pre>
  
  <p>why I get all the result is fast?</p>