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From "shao.hongxiao" <17611022...@163.com>
Subject Re: Flink Task Manager GC overhead limit exceeded
Date Fri, 01 May 2020 00:34:48 GMT
Please refer to this document [1] for more details   
能发一下具体链接吗,我也发现flink ui上显示的内存参数不太对,我想仔细看一下相关说明


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On 04/30/2020 12:08, Xintong Song wrote:
Then I would suggest the following.
- Check the task manager log to see if the '-D' properties are properly loaded. They should
be located at the beginning of the log file.
- You can also try to log into the pod and check the JVM launch command with "ps -ef | grep
TaskManagerRunner". I suspect there might be some argument passing problem regarding the spaces
and double quotation marks.

Thank you~

Xintong Song

On Thu, Apr 30, 2020 at 11:39 AM Eleanore Jin <eleanore.jin@gmail.com> wrote:

Hi Xintong, 

Thanks for the detailed explanation!

as for the 2nd question: I mount  it to am emptyDir, I assume pod restart will not cause the
pod to be rescheduled to another node, so it should stay?  I verified by directly adding this
to the flink-conf.yaml, which I see the heap dump is taken and stays in the directory:  env.java.opts:
-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/dumps

In addition, I also don't see the log print out something like: Heap dump file created [5220997112
bytes in 73.464 secs], which I see when directly adding the options in the flink-conf.yaml


- volumeMounts:

        - mountPath: /dumps

          name: heap-dumps


      - emptyDir: {}

        name: heap-dumps

Thanks a lot!


On Wed, Apr 29, 2020 at 7:55 PM Xintong Song <tonysong820@gmail.com> wrote:

Hi Eleanore,

I'd like to explain about 1 & 2. For 3, I have no idea either.

1. I dont see the heap size from UI for task manager show correctly

Despite the 'heap' in the key, 'taskmanager.heap.size' accounts for the total memory of a
Flink task manager, rather than only the heap memory. A Flink task manager process consumes
not only java heap memory, but also direct memory (e.g., network buffers) and native memory
(e.g., JVM overhead). That's why the JVM heap size shown on the UI is much smaller than the
configured 'taskmanager.heap.size'. Please refer to this document [1] for more details. This
document comes from Flink 1.9 and has not been back-ported to 1.8, but the contents should
apply to 1.8 as well.

2. I dont see the heap dump file in the restarted pod /dumps/oom.bin, did I set the java opts

The java options look good to me. It the configured path '/dumps/oom.bin' a local path of
the pod or a path of the host mounted onto the pod? The restarted pod is a completely new
different pod. Everything you write to the old pod goes away as the pod terminated, unless
they are written to the host through mounted storage.

Thank you~

Xintong Song

[1] https://ci.apache.org/projects/flink/flink-docs-release-1.9/ops/mem_setup.html

On Thu, Apr 30, 2020 at 7:41 AM Eleanore Jin <eleanore.jin@gmail.com> wrote:

Hi All, 

Currently I am running a flink job cluster (v1.8.2) on kubernetes with 4 pods, each pod with
4 parallelism. 

The flink job reads from a source topic with 96 partitions, and does per element filter, the
filtered value comes from a broadcast topic and it always use the latest message as the filter
criteria, then publish to a sink topic. 

There is no checkpointing and state involved. 

Then I am seeing GC overhead limit exceeded error continuously and the pods keep on restarting

So I tried to increase the heap size for task manager by


      - args:

        - task-manager

        - -Djobmanager.rpc.address=service-job-manager

        - -Dtaskmanager.heap.size=4096m

        - -Denv.java.opts.taskmanager="-XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/dumps/oom.bin"

3 things I noticed, 

1. I dont see the heap size from UI for task manager show correctly

2. I dont see the heap dump file in the restarted pod /dumps/oom.bin, did I set the java opts

3. I continously seeing below logs from all pods, not sure if causes any issue
{"@timestamp":"2020-04-29T23:39:43.387Z","@version":"1","message":"[Consumer clientId=consumer-1,
groupId=aba774bc] Node 6 was unable to process the fetch request with (sessionId=2054451921,
epoch=474): FETCH_SESSION_ID_NOT_FOUND.","logger_name":"org.apache.kafka.clients.FetchSessionHandler","thread_name":"pool-6-thread-1","level":"INFO","level_value":20000}

Thanks a lot for any help!

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