Single<Json.Result> searchRaw(ObjectNode query, Map<String, String> httpParams) {
      final Request request = new Request("POST", String.format("/%s/_search", index));
      httpParams.forEach(request::addParameter);
      request.setJsonEntity(query.toString());
      if (logger.isLoggable(Level.FINE)) {
        logger.log(Level.FINE, "Performing search {0} on {1}", new Object[] {query, request});
      }
      return transport.execute(request).map(r -> responseConverter().apply(r));
  }
Call {@code _count} endpoint to get count of documents matching a query.
@see <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/search-count.html">search-count</a>
criteria/elasticsearch/src/org/immutables/criteria/elasticsearch/ElasticsearchOps.java