sessions = CacheBuilder
                .newBuilder()
                .initialCapacity(30000)
                .maximumSize(5000000)
                .expireAfterAccess(session_ttl, TimeUnit.SECONDS)
                .removalListener((RemovalListener<String, Session>) notification -> {
                    Session session = notification.getValue();
                    if (session != null) {
                        logger.debug("Close session: " + notification.getKey());
                        session.close();
                    }
                })
                .build();