public SearchNodeMetricsResponse getSearchNodeMetrics(ApplicationId applicationId) {
        Application application = getApplication(applicationId);
        SearchNodeMetricsRetriever searchNodeMetricsRetriever = new SearchNodeMetricsRetriever();
        return searchNodeMetricsRetriever.getMetrics(application);
    }
Gets the active Session for the given application id.

@return the active session, or null if there is no active session for the given application id.
configserver/src/main/java/com/yahoo/vespa/config/server/ApplicationRepository.java