There are various methods for searching ES.
Simple performs a simple search that is limited to the number of returned documents. Be aware that there is a maximum query size on ES side that you can not affect on the client side. A query that would produce more results will not return all documents!
Scroll performs a scrolling search that basically paginates through all result pages and therefore overcoming the limits of a simple search.
Parallel performs a sliced scrolling search allowing to query Elasticsearch in parallel via Go routines.