title: Elasticsearch: auto increment integer field across two index
body: <p>I need a auto increment integer field across two index. </p>
  
  <p>Can Elasticsearch do it automatically like MySQL "auto increment" field in a table?</p>
  
  <p>Eg. when puts some documents in two different index:</p>
  
  <pre><code>POST /my_index_1/blogpost/
  {
    "title": "Foo Bar"
  }
  
  POST /my_index_2/blogpost/
  {
    "title": "Baz quux"
  }
  </code></pre>
  
  <p>On retrieve it, i want:</p>
  
  <pre><code>GET /my_index_*/blogpost/
  {
    "uid" : 1,
    "title": "Foo Bar"
  },
  {
    "uid" : 2,
    "title": "Baz quux"
  }
  </code></pre>