private boolean oldSessionDirWithUnknownStatus(Instant created, Session.Status status) {
        Duration expiryTime = Duration.ofHours(configserverConfig.keepSessionsWithUnknownStatusHours());
        return created != Instant.EPOCH // We don't know anything about creation time for this session
                && status == UNKNOWN
                && created.plus(expiryTime).isBefore(clock.instant());
    }
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