I've read in many places that updating nested documents will cause a reindex of the parent document.
But what I'm not clear on is if updating the parent document will cause a reindex of all the nested documents. It sounds like ES stores them as separate docs under the covers, and if the nested documents don't copy their fields to the parent "_all" or "_source", I think it won't need to reindex them?
What we're thinking about doing is moving our very large fields into nested documents, and have the more frequently changing fields in the root/parent document. We need this as we are way, way too often hitting the merge throttling limit, which just seems to shut down indexing completely.