title: elastic search primary key and secondary key
body: <p>I have an index in elastics search with products. Every product has an article number in the form of a guid. To show this products on a webshop I don't want to show a guid (to long). I want an integer number.</p>
  
  <p>Now i have two keys. One to lookup the web request (the integer) and one to update the product (the guid)</p>
  
  <p>I know I can search on a field in elastic search. But is an exact match search on a field slower as an exact match on a key (_id)? I don't want to do a mapping search from one key to the other because that is another operation.</p>