title: how to incrementally update nested objects in elasticsearch?
body: <p>I have 2 document types (in normal form in relational db):</p>
  
  <p>1: post (with title, text and author fields)</p>
  
  <p>2: comment (with text, author, post_id fields)</p>
  
  <p>I have only one type in elastic (post) that aggregate each post with all comments on them in nested form.</p>
  
  <p>I want to index posts with comments on it as nested objects for decreasing response time of queries but it will increase cost of indexing significantly if I reindex whole "post" document every time a new "comment" added, how can I handle it efficiently? It is acceptable for me to have data of comments with 1h delay.</p>
  
  <p>In fact it is three question:</p>
  
  <p><strong>1- how can I update a post document with only added comment data. (without need to reconstruct whole post document and send it to elastic)</strong> </p>
  
  <p><strong>2- how can I aggregate index commands that was related to a document and send it as a one single command to elastic?</strong></p>
  
  <p><strong>3- Is river plugin a solution for these? is it index comments without need to reconstruct whole post document? is it aggregate all updates related to one document and apply it with one index request?</strong></p>