Necessary to index a keyword field for exists query?

Hi,

Let us say, I have a User schema - name, address, bio and website. The website field is a keyword, but potentially unbounded - that is, the total number of all possible unique websites is limitless.

I am interested in making queries wherein I filter for users that have a website (most don't). I would need to index the website field for this filter, right? I am worried about indexing a keyword field with potentially unbounded unique terms. Will this blow up the index? Am I, instead, better off creating a derivative boolean field hasWebsite and indexing that one instead?

Take a look at the ignore_above mapping parameter.