if len(sys.peerClients) == 0 {
		return nil
	}
	peerClients := sys.allPeerClients
	if len(peerClients) == 0 {
		return nil
	}
	idx := xxhash.Sum64String(s) % uint64(len(peerClients))
	return peerClients[idx]
}

// GetPeerOnlineCount gets the count of online and offline nodes.
func (sys *NotificationSys) GetPeerOnlineCount() (nodesOnline, nodesOffline int) {