Hi I am trying to find how much time it took for a message on Kafka to be picked up by my Flink app. These two metrics seem relevant:

currentFetchEventTimeLag

and

currentEmitEventTimeLag

I can see the metric

currentEmitEventTimeLag

but not

currentFetchEventTimeLag

in Flink UI. Any idea why? What is the difference between the two? Will backpressure cause differences between them?