Hi - I'm trying to identify bottlenecks in my Flink streaming job, and am curious about the Back Pressure view in the job manager web UI. If there are already docs for Back Pressure please feel free to just point me to those. :)

When "Sampling in progress..." is displayed, what exactly is happening?

What do the values in the Ratio column for each Subtask mean exactly?

What does Status such as OK, High, etc mean? Are these determined from the Ratio values?

If my job graph looks like Source => A => B => Sink, with Back Pressure OK for Source and Sink, but High for A and B, what does that suggest?