We have a fairly large site 600k+ unique pages with various unique URLs along with a custom, local search interface for the site. The search interface has sorting and faceting capabilities to allow users to limit results and change display. **We are getting over 200,000 search requests a day from googlebot alone, and have tried to address it in the following ways:**

* adding noindex to faceting and sorting requests
* adding `rel=next` and `rel=prev` to results pages to allow google to understand structure

We are considering adding a sitemap.xml to ensure that content pages are found, and also attempting to add a ~~Dissallow~~ Disallow entry in the robots.txt for the search results. Does anyone have any experience with the effects of this? Ideally, we don't want to lose rankings or results in Google, but also would love to not suffer the impact of serving up 200k searches a day to a search engine bot that just wants real content and not search results.