Does Elasticsearch evaluate relevance scores of documents in parallel for one search request

Question

I have a native script to score documents. I'm wondering for a search request, are the documents scored by one thread (if a threadpool is used for search) or it's configurable to do that in parallel? (I know that docs on different nodes in the cluster can be scored in parallel. Here I mean in the same node).

Thanks

Answer 1

Documents belonging to the same shard are scored sequentially in a single thread. AFAIK, it cannot be configured to be done in parallel. Search operation across multiple shards potentially can happen in parallel whether they belong to the same node or different nodes.