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Posted to dev@flink.apache.org by "Robert Metzger (Jira)" <ji...@apache.org> on 2021/03/19 19:15:00 UTC

[jira] [Created] (FLINK-21884) Reduce TaskManager failure detection time

Robert Metzger created FLINK-21884:
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             Summary: Reduce TaskManager failure detection time
                 Key: FLINK-21884
                 URL: https://issues.apache.org/jira/browse/FLINK-21884
             Project: Flink
          Issue Type: Improvement
          Components: Runtime / Coordination
            Reporter: Robert Metzger
             Fix For: 1.14.0
         Attachments: image-2021-03-19-20-10-40-324.png

In Flink 1.13 (and older versions), TaskManager failures stall the processing for a significant amount of time, even though the system gets indications for the failure almost immediately through network connection losses.

This is due to a high (default) heartbeat timeout of 50 seconds [1] to accommodate for GC pauses, transient network disruptions or generally slow environments (otherwise, we would unregister a healthy TaskManager).

Such a high timeout can lead to disruptions in the processing (no processing for certain periods, high latencies, buildup of consumer lag etc.). In Reactive Mode (FLINK-10407), the issue surfaces on scale-down events, where the loss of a TaskManager is immediately visible in the logs, but the job is stuck in "FAILING" for quite a while until the TaskManger is really deregistered. (Note that this issue is not that critical in a autoscaling setup, because Flink can control the scale-down events and trigger them proactively)

On this metrics dashboard, one can see that the job has significant throughput drops / consumer lags during scale down (and also CPU usage spikes on processing the queued events, leading to incorrect scale up events again).
 !image-2021-03-19-20-10-40-324.png! 

One idea to solve this problem is to:
- Score TaskManagers based on certain signals (# exceptions reported, exception types (connection losses, akka failures), failure frequencies,  ...) and blacklist them accordingly.

[1] https://ci.apache.org/projects/flink/flink-docs-master/docs/deployment/config/#heartbeat-timeout






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