private void nodeChanged() {
        zkWatcherExecutor.execute(() -> {
            Multiset<Session.Status> sessionMetrics = HashMultiset.create();
            getRemoteSessions().forEach(session -> sessionMetrics.add(session.getStatus()));
            metricUpdater.setNewSessions(sessionMetrics.count(NEW));
            metricUpdater.setPreparedSessions(sessionMetrics.count(PREPARE));
            metricUpdater.setActivatedSessions(sessionMetrics.count(ACTIVATE));
            metricUpdater.setDeactivatedSessions(sessionMetrics.count(DEACTIVATE));
        });
    }
A session for which we don't have a watcher, i.e. hitherto unknown to us.

@param sessionId session id for the new session
configserver/src/main/java/com/yahoo/vespa/config/server/session/SessionRepository.java