title: ElasticSearch: post_filter or filter?
body: <p>Let's say I have a similar situation explained here:
  <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-post-filter.html" rel="noreferrer">https://www.elastic.co/guide/en/elasticsearch/reference/current/search-request-post-filter.html</a></p>
  
  <p>Before I stumbled upon this article, I have been using filter instead of post_filter for this kind of scenario, and it produced output just like the post_filter.</p>
  
  <p>My question is: Are they the same thing? If not, which one is the recommended and more efficient method to use and why?</p>