title: What does "Limit of total fields [1000] in index [] has been exceeded" means in Elasticsearch
body: <p>I have Elasticsearch index created which has approx 350 fields (Including nested fields) , I have defined mapping only for few of them. 
  While calling _update API I am getting below exception with 400 Bad request.</p>
  
  <p><strong>Limit of total fields [1000] in index [test_index] has been exceeded</strong><br>
  I want to understand the exact reason for this exception since my number of fields and fields for which mapping is defined both are less than 1000.<br>
  <strong>Note:</strong> I have nested fields and dynamic mapping enabled. </p>
  
  <p>Regards,<br>
  Sandeep</p>