zhijiangW commented on a change in pull request #10083:
[FLINK-14472][runtime]Implement back-pressure monitor with non-blocking outputs.
URL: https://github.com/apache/flink/pull/10083#discussion_r346110747
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File path: docs/monitoring/back_pressure.md
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@@ -34,30 +34,28 @@ If you see a **back pressure warning** (e.g. `High`) for a
task, this means that
Take a simple `Source -> Sink` job as an example. If you see a warning for
`Source`, this means that `Sink` is consuming data slower than `Source` is
producing. `Sink` is back pressuring the upstream operator `Source`.
-## Sampling Threads
+## Sampling Tasks
-Back pressure monitoring works by repeatedly taking stack trace samples of
your running tasks. The JobManager triggers repeated calls to
`Thread.getStackTrace()` for the tasks of your job.
+Back pressure monitoring works by repeatedly taking samples of your running
tasks. The JobManager triggers repeated calls to `Task.isBackPressured()` for
the tasks of your job.
<img src="{{ site.baseurl }}/fig/back_pressure_sampling.png"
class="img-responsive">
-<!--
https://docs.google.com/drawings/d/1_YDYGdUwGUck5zeLxJ5Z5jqhpMzqRz70JxKnrrJUltA/edit?usp=sharing
-->
+<!--
https://docs.google.com/drawings/d/1O5Az3Qq4fgvnISXuSf-MqBlsLDpPolNB7EQG7A3dcTk/edit?usp=sharing
-->
-If the samples show that a task Thread is stuck in a certain internal method
call (requesting buffers from the network stack), this indicates that there is
back pressure for the task.
Review comment:
Add some introductions of how to judge the back pressure state instead.
E.g. Internally we judge the back pressure based on the availability of
output buffers. If there are no available buffers for at-least one output, then
it indicates that there is back pressure for the task.
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