@Query("SELECT * FROM conversations")
Flowable<List<ConversationItem>> getConversations();

conversationsDatabase.getConversations()
       .observeOn(AndroidSchedulers.mainThread())
        .subscribeOn(Schedulers.io())
        .subscribe(conversations -> {
                   long endTime = System.nanoTime();
                   long duration = (endTime - startTime);
                   Timber.d("load conversation time: " + duration);
                });