flink-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Tony Wei <tony19920...@gmail.com>
Subject Re: Stream Task seems to be blocked after checkpoint timeout
Date Thu, 28 Sep 2017 09:25:20 GMT
Hi Stefan,

These are some telemetry information, but I don't have history information
about gc.

[image: 內置圖片 2]
[image: 內置圖片 1]

1) Yes, my state is not large.
2) My DFS is S3, but my cluster is out of AWS. It might be a problem. Since
this is a POC, we might move to AWS in the future or use HDFS in the same
cluster. However, how can I recognize the problem is this.
3) It seems memory usage is bounded. I'm not sure if the status showed
above is fine.

There is only one TM in my cluster for now, so all tasks are running on
that machine. I think that means they are in the same JVM, right?
Besides taking so long on asynchronous part, there is another question is
that the late message showed that this task was delay for almost 7 minutes,
but the log showed it only took 4 minutes.
It seems that it was somehow waiting for being executed. Are there some
points to find out what happened?

For the log information, what I means is it is hard to recognize which
checkpoint id that asynchronous parts belong to if the checkpoint takes
more time and there are more concurrent checkpoints taking place.
Also, it seems that asynchronous part might be executed right away if there
is no resource from thread pool. It is better to measure the time between
creation time and processing time, and log it and checkpoint id with the
original log that showed what time the asynchronous part took.

Best Regards,
Tony Wei

2017-09-28 16:25 GMT+08:00 Stefan Richter <s.richter@data-artisans.com>:

> Hi,
>
> when the async part takes that long I would have 3 things to look at:
>
> 1) Is your state so large? I don’t think this applies in your case, right?
> 2) Is something wrong with writing to DFS (network, disks, etc)?
> 3) Are we running low on memory on that task manager?
>
> Do you have telemetry information about used heap and gc pressure on the
> problematic task? However, what speaks against the memory problem
> hypothesis is that future checkpoints seem to go through again. What I find
> very strange is that within the reported 4 minutes of the async part the
> only thing that happens is: open dfs output stream, iterate the in-memory
> state and write serialized state data to dfs stream, then close the stream.
> No locks or waits in that section, so I would assume that for one of the
> three reasons I gave, writing the state is terribly slow.
>
> Those snapshots should be able to run concurrently, for example so that
> users can also take savepoints  even when a checkpoint was triggered and is
> still running, so there is no way to guarantee that the previous parts have
> finished, this is expected behaviour. Which waiting times are you missing
> in the log? I think the information about when a checkpoint is triggered,
> received by the TM, performing the sync and async part and acknowledgement
> time should all be there?.
>
> Best,
> Stefan
>
>
>
> Am 28.09.2017 um 08:18 schrieb Tony Wei <tony19920430@gmail.com>:
>
> Hi Stefan,
>
> The checkpoint on my job has been subsumed again. There are some questions
> that I don't understand.
>
> Log in JM :
> 2017-09-27 13:45:15,686 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Completed checkpoint 1576 (174693180 bytes in 21597 ms).
> 2017-09-27 13:49:42,795 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Triggering checkpoint 1577 @ 1506520182795
> 2017-09-27 13:54:42,795 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Triggering checkpoint 1578 @ 1506520482795
> 2017-09-27 13:55:13,105 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Completed checkpoint 1578 (152621410 bytes in 19109 ms).
> 2017-09-27 13:56:37,103 WARN org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Received late message for now expired checkpoint attempt 1577 from
> 2273da50f29b9dee731f7bd749e91c80 of job 7c039572b....
> 2017-09-27 13:59:42,795 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
> - Triggering checkpoint 1579 @ 1506520782795
>
> Log in TM:
> 2017-09-27 13:56:37,105 INFO org.apache.flink.runtime.state.DefaultOperatorStateBackend
> - DefaultOperatorStateBackend snapshot (File Stream Factory @
> s3://tony-dev/flink-checkpoints/7c039572b13346f1b17dcc0ace2b72c2,
> asynchronous part) in thread Thread[pool-7-thread-322,5,Flink Task
> Threads] took 240248 ms.
>
> I think the log in TM might be the late message for #1577 in JM, because
> #1576, #1578 had been finished and #1579 hadn't been started at 13:56:37.
> If there is no mistake on my words, I am wondering why the time it took
> was 240248 ms (4 min). It seems that it started late than asynchronous
> tasks in #1578.
> Is there any way to guarantee the previous asynchronous parts of
> checkpoints will be executed before the following.
>
> Moreover, I think it will be better to have more information in INFO log,
> such as waiting time and checkpoint id, in order to trace the progress of
> checkpoint conveniently.
>
> What do you think? Do you have any suggestion for me to deal with these
> problems? Thank you.
>
> Best Regards,
> Tony Wei
>
> 2017-09-27 17:11 GMT+08:00 Tony Wei <tony19920430@gmail.com>:
>
>> Hi Stefan,
>>
>> Here is the summary for my streaming job's checkpoint after restarting at
>> last night.
>>
>> <???? 2017-09-2 7 下午4.56.30.png>
>>
>> This is the distribution of alignment buffered from the last 12 hours.
>>
>> <???? 2017-09-2 7 下午5.05.11.png>
>>
>> And here is the buffer out pool usage during chk #1140 ~ #1142. For chk
>> #1245 and #1246, you can check the picture I sent before.
>>
>>  <???? 2017-09-2 7 下午5.01.24.png>
>>
>> AFAIK, the back pressure rate usually is in LOW status, sometimes goes up
>> to HIGH, and always OK during the night.
>>
>> Best Regards,
>> Tony Wei
>>
>>
>> 2017-09-27 16:54 GMT+08:00 Stefan Richter <s.richter@data-artisans.com>:
>>
>>> Hi Tony,
>>>
>>> are your checkpoints typically close to the timeout boundary? From what
>>> I see, writing the checkpoint is relatively fast but the time from the
>>> checkpoint trigger to execution seems very long. This is typically the case
>>> if your job has a lot of backpressure and therefore the checkpoint barriers
>>> take a long time to travel to the operators, because a lot of events are
>>> piling up in the buffers. Do you also experience large alignments for your
>>> checkpoints?
>>>
>>> Best,
>>> Stefan
>>>
>>> Am 27.09.2017 um 10:43 schrieb Tony Wei <tony19920430@gmail.com>:
>>>
>>> Hi Stefan,
>>>
>>> It seems that I found something strange from JM's log.
>>>
>>> It had happened more than once before, but all subtasks would finish
>>> their checkpoint attempts in the end.
>>>
>>> 2017-09-26 01:23:28,690 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Triggering checkpoint 1140 @ 1506389008690
>>> 2017-09-26 01:28:28,690 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Triggering checkpoint 1141 @ 1506389308690
>>> 2017-09-26 01:33:28,690 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Triggering checkpoint 1142 @ 1506389608690
>>> 2017-09-26 01:33:28,691 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Checkpoint 1140 expired before completing.
>>> 2017-09-26 01:38:28,691 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Checkpoint 1141 expired before completing.
>>> 2017-09-26 01:40:38,044 WARN org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Received late message for now expired checkpoint attempt 1140 from
>>> c63825d15de0fef55a1d148adcf4467e of job 7c039572b...
>>> 2017-09-26 01:40:53,743 WARN org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Received late message for now expired checkpoint attempt 1141 from
>>> c63825d15de0fef55a1d148adcf4467e of job 7c039572b...
>>> 2017-09-26 01:41:19,332 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Completed checkpoint 1142 (136733704 bytes in 457413 ms).
>>>
>>> For chk #1245 and #1246, there was no late message from TM. You can
>>> refer to the TM log. The full completed checkpoint attempt will have 12
>>> (... asynchronous part) logs in general, but #1245 and #1246 only got 10
>>> logs.
>>>
>>> 2017-09-26 10:08:28,690 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Triggering checkpoint 1245 @ 1506420508690
>>> 2017-09-26 10:13:28,690 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Triggering checkpoint 1246 @ 1506420808690
>>> 2017-09-26 10:18:28,691 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Checkpoint 1245 expired before completing.
>>> 2017-09-26 10:23:28,691 INFO org.apache.flink.runtime.checkpoint.CheckpointCoordinator
>>> - Checkpoint 1246 expired before completing.
>>>
>>> Moreover, I listed the directory for checkpoints on S3 and saw there
>>> were two states not discarded successfully. In general, there will be 16
>>> parts for a completed checkpoint state.
>>>
>>> 2017-09-26 18:08:33 36919 tony-dev/flink-checkpoints/7c0
>>> 39572b13346f1b17dcc0ace2b72c2/chk-1245/eedd7ca5-ee34-45a5-bf
>>> 0b-11cc1fc67ab8
>>> 2017-09-26 18:13:34 37419 tony-dev/flink-checkpoints/7c0
>>> 39572b13346f1b17dcc0ace2b72c2/chk-1246/9aa5c6c4-8c74-465d-85
>>> 09-5fea4ed25af6
>>>
>>> Hope these informations are helpful. Thank you.
>>>
>>> Best Regards,
>>> Tony Wei
>>>
>>> 2017-09-27 16:14 GMT+08:00 Stefan Richter <s.richter@data-artisans.com>:
>>>
>>>> Hi,
>>>>
>>>> thanks for the information. Unfortunately, I have no immediate idea
>>>> what the reason is from the given information. I think most helpful could
>>>> be a thread dump, but also metrics on the operator operator level to figure
>>>> out which part of the pipeline is the culprit.
>>>>
>>>> Best,
>>>> Stefan
>>>>
>>>> Am 26.09.2017 um 17:55 schrieb Tony Wei <tony19920430@gmail.com>:
>>>>
>>>> Hi Stefan,
>>>>
>>>> There is no unknown exception in my full log. The Flink version is
>>>> 1.3.2.
>>>> My job is roughly like this.
>>>>
>>>> env.addSource(Kafka)
>>>>   .map(ParseKeyFromRecord)
>>>>   .keyBy()
>>>>   .process(CountAndTimeoutWindow)
>>>>   .asyncIO(UploadToS3)
>>>>   .addSink(UpdateDatabase)
>>>>
>>>> It seemed all tasks stopped like the picture I sent in the last email.
>>>>
>>>> I will keep my eye on taking a thread dump from that JVM if this
>>>> happens again.
>>>>
>>>> Best Regards,
>>>> Tony Wei
>>>>
>>>> 2017-09-26 23:46 GMT+08:00 Stefan Richter <s.richter@data-artisans.com>
>>>> :
>>>>
>>>>> Hi,
>>>>>
>>>>> that is very strange indeed. I had a look at the logs and there is no
>>>>> error or exception reported. I assume there is also no exception in your
>>>>> full logs? Which version of flink are you using and what operators were
>>>>> running in the task that stopped? If this happens again, would it be
>>>>> possible to take a thread dump from that JVM?
>>>>>
>>>>> Best,
>>>>> Stefan
>>>>>
>>>>> > Am 26.09.2017 um 17:08 schrieb Tony Wei <tony19920430@gmail.com>:
>>>>> >
>>>>> > Hi,
>>>>> >
>>>>> > Something weird happened on my streaming job.
>>>>> >
>>>>> > I found my streaming job seems to be blocked for a long time and
I
>>>>> saw the situation like the picture below. (chk #1245 and #1246 were all
>>>>> finishing 7/8 tasks then marked timeout by JM. Other checkpoints failed
>>>>> with the same state like #1247 util I restarted TM.)
>>>>> >
>>>>> > <snapshot.png>
>>>>> >
>>>>> > I'm not sure what happened, but the consumer stopped fetching
>>>>> records, buffer usage is 100% and the following task did not seem to
fetch
>>>>> data anymore. Just like the whole TM was stopped.
>>>>> >
>>>>> > However, after I restarted TM and force the job restarting from
the
>>>>> latest completed checkpoint, everything worked again. And I don't know
how
>>>>> to reproduce it.
>>>>> >
>>>>> > The attachment is my TM log. Because there are many user logs and
>>>>> sensitive information, I only remain the log from `org.apache.flink...`.
>>>>> >
>>>>> > My cluster setting is one JM and one TM with 4 available slots.
>>>>> >
>>>>> > Streaming job uses all slots, checkpoint interval is 5 mins and
max
>>>>> concurrent number is 3.
>>>>> >
>>>>> > Please let me know if it needs more information to find out what
>>>>> happened on my streaming job. Thanks for your help.
>>>>> >
>>>>> > Best Regards,
>>>>> > Tony Wei
>>>>> > <flink-root-taskmanager-0-partial.log>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>
>

Mime
View raw message