how to Get message backlog？

I successfully obtained data using RocketMQ Exporter, but I am unable to determine which value corresponds to message backlog. Could you please inform me of the corresponding value? Thank you.
我目前成功的使用rocketmq-exporter获取到了服务信息，但是不知道消息积压的key对应的是哪个，大佬们知道的告知下，镜像版本是最新的。