code: private static void configureRouting(IssueQuery query, SearchOptions options, SearchRequestBuilder requestBuilder) {
      Collection<String> uuids = query.projectUuids();
      if (!uuids.isEmpty() && options.getFacets().isEmpty()) {
        requestBuilder.setRouting(uuids.stream().map(AuthorizationDoc::idOf).toArray(String[]::new));
      }
    }
docs: Optimization - do not send ES request to all shards when scope is restricted
  to a set of projects. Because project UUID is used for routing, the request
  can be sent to only the shards containing the specified projects.
  Note that sticky facets may involve all projects, so this optimization must be
  disabled when facets are enabled.