[GitHub] [flink] pnowojski commented on pull request #14526: [FLINK-14814][WebUI] Highlight back pressured and busy nodes in the WebUI

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pnowojski commented on pull request #14526:
URL: https://github.com/apache/flink/pull/14526#issuecomment-754068307


   > On startup, values are Nan and sometimes all boxes are red
   
   NaNs I think come from the WebUI, when it hasn't yet managed to update those values. I think it's better to display them as `NaN` as oppose of picking some unknown values.
   
   Boxes are red until the first update of metric views. Until then, `idleTime` and `backPressuredTime` are zero, so by definition `busyTime` is `1000ms/s`.
    
   > "Busy (max)" label - this shounds to me like max in time, not across subtasks
   
   How would you rename this label?
   
   > For sources, Busy time is always NaN% (can we remove volatile busyTimeEnabled?)
   
   That's by design. I thought it's better to display `NaN%` to clearly indicate value couldn't not be calculated instead of calculating `0`.
    
   > With DataStreammAllRoundTestJob, mapper is almost as busy as it's upstream sliding window (76% vs 84%) - this seems strange to me
   
   If not for the load spikes from `WindowOperator`, this would be probably 100% busy for upstream and ~90% busy for the downstream operator. And that I think would be expected if downstream operator is barely keeping up.
   
   If you add the load spikes from `WindowOperator` to the mix, I think the explanation is similar. Downstream operator is barely keeping up overall (on average), however during the load spikes downstream is the bottleneck, back-pressuring the the `WindowOperator`. This I think explains that mapper is idling ~24% of time, with ~76% busy, while `WindowOperator` is idling 0% of the time, with ~17% backpressured and ~83% busy.


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