title: Elasticsearch: count returning wrong value
body: <p>ES 1.7.3</p>
  
  <p>We have around 20M documents. Each document has a unique ID. When we do a count-request (/index/type/_count) we get around 30K less documents than we indexed.</p>
  
  <p>I checked the existence of each document by making requests on the ID field. Result: there is none missing.</p>
  
  <p>Is there any reasons why <code>_count</code> returns not the exact count?</p>
  
  <p>PS: I read about estimates when doing aggregations. Is this perhaps related?</p>