Hi Xingbo,

thanks for taking care and letting me know. I was about to share an example, 
how to reproduce this.
Now I will wait for the next release candidate and give it a try.

Regards,
Niklas


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> On 26. Nov 2020, at 02:59, Xingbo Huang <hxbks...@gmail.com> wrote:
> 
> Hi Niklas,
> 
> Regarding `Exception in thread "grpc-nio-worker-ELG-3-2" 
> java.lang.NoClassDefFoundError: 
> org/apache/beam/vendor/grpc/v1p26p0/io/netty/buffer/PoolArena$1`, 
> it does not affect the correctness of the result. The reason is that some 
> resources are released asynchronously when Grpc Server is shut down[1] . 
> After the UserClassLoader unloads the class, the asynchronous thread tries to 
> release the resources and throw NotClassFoundException, but the content of 
> the data result has been sent downstream, so the correctness of the result 
> will not be affected.
> 
> Regarding the details of the specific causes, I have explained in the flink 
> community[2] and the beam community[3], and fixed them in the flink 
> community. There will be no such problem in the next version of release 
> 1.11.3 and 1.12.0.
> 
> [1] 
> https://github.com/grpc/grpc-java/blob/master/core/src/main/java/io/grpc/internal/SharedResourceHolder.java#L150
>  
> <https://github.com/grpc/grpc-java/blob/master/core/src/main/java/io/grpc/internal/SharedResourceHolder.java#L150>
> [2] https://issues.apache.org/jira/browse/FLINK-20284 
> <https://issues.apache.org/jira/browse/FLINK-20284>
> [3] https://issues.apache.org/jira/browse/BEAM-5397 
> <https://issues.apache.org/jira/browse/BEAM-5397>
> 
> Best,
> Xingbo
> 
> 
> Dian Fu <dian0511...@gmail.com <mailto:dian0511...@gmail.com>> 于2020年11月16日周一 
> 下午9:10写道:
> Hi Niklas,
> 
>> How can I ingest data in a batch table from Kafka or even better 
>> Elasticsearch. Kafka is only offering a Streaming source and Elasticsearch 
>> isn't offering a source at all.
>> The only workaround which comes to my mind is to use the Kafka streaming 
>> source and to apply a single very large window to create a bounded table. Do 
>> you think that would work?
>> Are there other options available? Maybe converting a Stream to a bounded 
>> table is somehow possible? Thank you!
> 
> 
> I think you are right that Kafka still doesn't support batch and there is no 
> ES source for now. Another option is you could load the data into a connector 
> which supports batch. Not sure if anybody else has a better idea about this.
> 
>> I found one cause of this problem and it was mixing a Scala 2.12 Flink 
>> installation with PyFlink, which has some 2.11 jars in its opt folder. I 
>> think the JVM just skipped the class definitions, because they weren't 
>> compatible. I actually wasn't aware of the fact that PyFlink comes with 
>> prebuilt jar dependencies. If PyFlink is only compatible with Scala 2.11 it 
>> would make sense to point that out in the documentation. I think I never 
>> read that and it might be missing. Unfortunately there is still one 
>> Exception showing up at the very end of the job in the taskmanager log. I 
>> did the verification you asked for and the class is present in both jar 
>> files. The one which comes with Flink in the opt folder and the one of 
>> PyFlink. You can find the log attached.
>> I think the main question is which jar file has be loaded in in the three 
>> envronments (executor, jobmanager, taskmanager). Is it fine to not put the 
>> flink-python_2.11-1.12.0.jar into the lib folder in the jobmanager and 
>> taskmanager? Will it somehow be transferred by PyFlink to the jobmanager and 
>> taskmanager?
> 
> PyFlink comes with the built-in jars such as flink-python_2.11-1.12.0.jar, 
> flink-dist_2.11-1.12.0.jar, etc and so you don't need to manually add 
> them(also shouldn't do that). Could you remove the duplicate jars and try it 
> again?
> 
>> No I don't think that there are additional exceptions besides 
>> "org.apache.beam.vendor.grpc.v1p26p0.io.grpc.StatusRuntimeException", but 
>> maybe take a look in the attached log files. This problem could be related 
>> to 2., maybe the root cause is a class loading issue as well. What do you 
>> think? You can find attached three log files. One for the executor, the 
>> jobmanager and the taskmanager. Maybe you can find something useful.
> 
> 
> I found one similar issue at Beam side: 
> https://issues.apache.org/jira/browse/BEAM-6258 
> <https://issues.apache.org/jira/browse/BEAM-6258> which has been resolved 
> long time ago. I'm still trying to reproduce this issue and will let you know 
> if there is any progress. (Would be great if you could help to provide an 
> example which could easily reproduce this issue)
> 
>> This was very helpful. I was able to implement it. There is only one detail 
>> missing. Is it possible to UNNEST an array of Rows or tuples? It would be 
>> really great if I would be able to return a list with multiple fields. 
>> Currently I'm just putting multiple value into a single VARCHAR, but that 
>> means the information needs to be extracted later on. Maybe you have an idea 
>> how to avoid that.
> 
> Currently, Pandas UDAF still doesn't support complex type and so I'm afraid 
> that you have to put multiple values into a single VARCHAR for now.
> 
> Regards,
> Dian
> 
> 
>> 在 2020年11月16日,上午2:46,Niklas Wilcke <niklas.wil...@uniberg.com 
>> <mailto:niklas.wil...@uniberg.com>> 写道:
>> 
>> Hi Dian,
>> 
>> this was very helpful again. To the old questions I will answer inline as 
>> well. Unfortunately also one new question popped up.
>> 
>> How can I ingest data in a batch table from Kafka or even better 
>> Elasticsearch. Kafka is only offering a Streaming source and Elasticsearch 
>> isn't offering a source at all.
>> The only workaround which comes to my mind is to use the Kafka streaming 
>> source and to apply a single very large window to create a bounded table. Do 
>> you think that would work?
>> Are there other options available? Maybe converting a Stream to a bounded 
>> table is somehow possible? Thank you!
>> 
>> Kind Regards,
>> Niklas
>> 
>> 
>> 
>>> On 13. Nov 2020, at 16:07, Dian Fu <dian0511...@gmail.com 
>>> <mailto:dian0511...@gmail.com>> wrote:
>>> 
>>> Hi Niklas,
>>> 
>>> Good to know that this solution may work for you. Regarding to the 
>>> questions you raised, please find my reply inline.
>>> 
>>> Regards,
>>> Dian
>>> 
>>>> 在 2020年11月13日,下午8:48,Niklas Wilcke <niklas.wil...@uniberg.com 
>>>> <mailto:niklas.wil...@uniberg.com>> 写道:
>>>> 
>>>> Hi Dian,
>>>> 
>>>> thanks again for your response. In the meantime I tried out your proposal 
>>>> using the UDAF feature of PyFlink 1.12.0-rc1 and it is roughly working, 
>>>> but I am facing some issues, which I would like to address. If this goes 
>>>> too far, please let me know and I will open a new thread for each of the 
>>>> questions. Let me share some more information about my current 
>>>> environment, which will maybe help to answer the questions. I'm currently 
>>>> using my dev machine with Docker and one jobmanager container and one 
>>>> taskmanager container. If needed I can share the whole docker environment, 
>>>> but this would involve some more effort on my side. Here are my five 
>>>> questions.
>>>> 
>>>> 1. Where can I find connector libraries for 1.12.0-rc1 or some kind of 
>>>> instruction how to build them? I can't find them in the 1.12.0-rc1 release 
>>>> and when I build flink from source, I can't find the connector libraries 
>>>> in the build target. I need flink-sql-connector-elasticsearch7 and 
>>>> flink-sql-connector-kafka.
>>> 
>>> You could download the connector jars of 1.12.0-rc1 from here: 
>>> https://repository.apache.org/content/repositories/orgapacheflink-1402/org/apache/flink/
>>>  
>>> <https://repository.apache.org/content/repositories/orgapacheflink-1402/org/apache/flink/>
>> Thanks that worked like a charm!
>> 
>>> 
>>>> 2. Which steps are needed to properly Setup PyFlink? I followed the 
>>>> instructions, but I always get some ClassNotFoundExceptions for some Beam 
>>>> related classes in the taskmanager. The job still works fine, but this 
>>>> doesn't look good to me. It happens in 1.11.2 and in 1.12.0-rc1. I tried 
>>>> to resolve this by adding certain jars, but I wasn't able to fix it. Maybe 
>>>> you have an idea. You can find the Dockerfile attached, which lines out 
>>>> the steps I'm currently using. The Exceptions signature looks like this.
>>>>    Exception in thread "grpc-nio-worker-ELG-3-2" 
>>>> java.lang.NoClassDefFoundError: 
>>>> org/apache/beam/vendor/grpc/v1p26p0/io/netty/buffer/PoolArena$1
>>> 
>>> Usually there is nothing specially need to do to set up PyFlink. I have 
>>> manually checked that this class should be there(inside 
>>> flink-python_2.11-1.12.0.jar) and so guess if it's because you environment 
>>> isn't clean enough? 
>>> 
>>> I guess you could check the following things:
>>> 1) Is it because you have installed 1.11.2 before and so the environment is 
>>> not clean enough? Could you uninstall PyFlink 1.11.2 manually and reinstall 
>>> PyFlink 1.12.0-rc1 again? You could also manually check that there should 
>>> be only one flink-python*.jar under directory xxx/site-packages/pyflink/opt/
>>> 2) Verify that the class is actually there by the following command: 
>>> (flink-python_2.11-1.12.0.jar is under directory 
>>> xxx/site-packages/pyflink/opt/)
>>>     jar tf flink-python_2.11-1.12.0.jar | grep 
>>> "org/apache/beam/vendor/grpc/v1p26p0/io/netty/buffer/PoolArena"
>>> 3) If this exception still happens, could you share the exception stack?
>> 
>> I found one cause of this problem and it was mixing a Scala 2.12 Flink 
>> installation with PyFlink, which has some 2.11 jars in its opt folder. I 
>> think the JVM just skipped the class definitions, because they weren't 
>> compatible. I actually wasn't aware of the fact that PyFlink comes with 
>> prebuilt jar dependencies. If PyFlink is only compatible with Scala 2.11 it 
>> would make sense to point that out in the documentation. I think I never 
>> read that and it might be missing. Unfortunately there is still one 
>> Exception showing up at the very end of the job in the taskmanager log. I 
>> did the verification you asked for and the class is present in both jar 
>> files. The one which comes with Flink in the opt folder and the one of 
>> PyFlink. You can find the log attached.
>> I think the main question is which jar file has be loaded in in the three 
>> envronments (executor, jobmanager, taskmanager). Is it fine to not put the 
>> flink-python_2.11-1.12.0.jar into the lib folder in the jobmanager and 
>> taskmanager? Will it somehow be transferred by PyFlink to the jobmanager and 
>> taskmanager?
>> 
>>> 
>>>> 3. When increasing the size of the input data set I get the following 
>>>> Exception and the job is canceled. I tried to increase the resources 
>>>> assigned to flink, but it didn't help. Do you have an idea why this is 
>>>> happening? You can find a more detailed stack trace in apendix.
>>> 
>>> Could you check if there are any other exceptions in the log when this 
>>> exception happens?
>> 
>> No I don't think that there are additional exceptions besides 
>> "org.apache.beam.vendor.grpc.v1p26p0.io.grpc.StatusRuntimeException", but 
>> maybe take a look in the attached log files. This problem could be related 
>> to 2., maybe the root cause is a class loading issue as well. What do you 
>> think? You can find attached three log files. One for the executor, the 
>> jobmanager and the taskmanager. Maybe you can find something useful.
>> 
>>> 
>>>> 4. I can't manage to get the SQL UNNEST operation to work. It is quite 
>>>> hard for me to debug it and I can't really find any valuable examples or 
>>>> documentation on the internet. Currently instead of creating an ARRAY I'm 
>>>> just returning a VARCHAR containing a string representation of the array. 
>>>> The relevant code you can find in the apendix.
>>> 
>>> There are some examples here: 
>>> https://github.com/apache/flink/blob/c601cfd662c2839f8ebc81b80879ecce55a8cbaf/flink-table/flink-table-planner-blink/src/test/scala/org/apache/flink/table/planner/runtime/batch/sql/UnnestITCase.scala
>>>  
>>> <https://github.com/apache/flink/blob/c601cfd662c2839f8ebc81b80879ecce55a8cbaf/flink-table/flink-table-planner-blink/src/test/scala/org/apache/flink/table/planner/runtime/batch/sql/UnnestITCase.scala>
>> 
>> This was very helpful. I was able to implement it. There is only one detail 
>> missing. Is it possible to UNNEST an array of Rows or tuples? It would be 
>> really great if I would be able to return a list with multiple fields. 
>> Currently I'm just putting multiple value into a single VARCHAR, but that 
>> means the information needs to be extracted later on. Maybe you have an idea 
>> how to avoid that.
>> 
>>> 
>>>> 5. How can I obtain the output of the Python interpreter executing the 
>>>> UDF. If I put a print statement in the UDF I can't see the output in the 
>>>> log of the taskmanager. Is there a way to access it?
>>> 
>>> You can use the standard logging in Python UDF instead of print. The log 
>>> output could then be found in the log of the task manager.
>> 
>> Thank you! That worked well. I should have checked that without asking.
>> 
>>> 
>>>> I hope these aren't too many questions for this thread. If this is the 
>>>> case I can still split some of them out. Please let me know, if this is 
>>>> the case.
>>>> Thank you very much. I really appreciate your help.
>>> 
>>> It's fine to reuse this thread. :)
>>> 
>>>> Kind Regards,
>>>> Niklas
>>>> 
>>>> 
>> 
>> End of the Taskmanager Log for 2.
>> ###################################################################
>> taskmanager_1    | 2020-11-15 17:46:53,438 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:5, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: e5137050c0f1ef5e660311ddf1f3429f, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,440 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:1, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: 541ad3e383fb9c024141f2bab5e8b7fd, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,442 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:2, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: ef8adb7d879f4072123fe4bc12054c0c, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,444 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:4, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: db5d62b8c9fe8172fc1883c148b150e8, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,846 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:0, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: 637d053a0726548c2bc9261fc0e55414, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,849 INFO  
>> org.apache.flink.runtime.taskexecutor.slot.TaskSlotTableImpl [] - Free slot 
>> TaskSlot(index:3, state:ACTIVE, resource profile: 
>> ResourceProfile{cpuCores=1.0000000000000000, taskHeapMemory=219.333mb 
>> (229987662 bytes), taskOffHeapMemory=166.667mb (174762666 bytes), 
>> managedMemory=342.933mb (359591667 bytes), networkMemory=85.733mb (89897916 
>> bytes)}, allocationId: cfaa8633b9102e3a509cfc94dd97d38f, jobId: 
>> ba4e3974860af7dc00a28fdfbb44fe06).
>> taskmanager_1    | 2020-11-15 17:46:53,851 INFO  
>> org.apache.flink.runtime.taskexecutor.DefaultJobLeaderService [] - Remove 
>> job ba4e3974860af7dc00a28fdfbb44fe06 from job leader monitoring.
>> taskmanager_1    | 2020-11-15 17:46:53,851 INFO  
>> org.apache.flink.runtime.taskexecutor.TaskExecutor           [] - Close 
>> JobManager connection for job ba4e3974860af7dc00a28fdfbb44fe06.
>> taskmanager_1    | 2020-11-15 17:46:54,371 ERROR 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.rejectedExecution
>>  [] - Failed to submit a listener notification task. Event loop shut down?
>> taskmanager_1    | java.lang.NoClassDefFoundError: 
>> org/apache/beam/vendor/grpc/v1p26p0/io/netty/util/concurrent/GlobalEventExecutor$2
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.GlobalEventExecutor.startThread(GlobalEventExecutor.java:227)
>>  
>> ~[blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.GlobalEventExecutor.execute(GlobalEventExecutor.java:215)
>>  
>> ~[blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.safeExecute(DefaultPromise.java:841)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.notifyListeners(DefaultPromise.java:498)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.setValue0(DefaultPromise.java:615)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.setSuccess0(DefaultPromise.java:604)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.DefaultPromise.setSuccess(DefaultPromise.java:96)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.SingleThreadEventExecutor$6.run(SingleThreadEventExecutor.java:1089)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
>>  
>> [blob_p-2cc5d5ac59c7842f512002d81251a3cbfed058cc-e14fe009bc07ddff407ea4c5d74bd4be:1.12.0]
>> taskmanager_1    |      at java.lang.Thread.run(Thread.java:748) 
>> [?:1.8.0_275]
>> taskmanager_1    | Caused by: java.lang.ClassNotFoundException: 
>> org.apache.beam.vendor.grpc.v1p26p0.io.netty.util.concurrent.GlobalEventExecutor$2
>> taskmanager_1    |      at 
>> java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[?:1.8.0_275]
>> taskmanager_1    |      at 
>> java.lang.ClassLoader.loadClass(ClassLoader.java:418) ~[?:1.8.0_275]
>> taskmanager_1    |      at 
>> org.apache.flink.util.FlinkUserCodeClassLoader.loadClassWithoutExceptionHandling(FlinkUserCodeClassLoader.java:63)
>>  ~[flink-dist_2.11-1.12.0.jar:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.flink.util.ChildFirstClassLoader.loadClassWithoutExceptionHandling(ChildFirstClassLoader.java:72)
>>  ~[flink-dist_2.11-1.12.0.jar:1.12.0]
>> taskmanager_1    |      at 
>> org.apache.flink.util.FlinkUserCodeClassLoader.loadClass(FlinkUserCodeClassLoader.java:49)
>>  ~[flink-dist_2.11-1.12.0.jar:1.12.0]
>> taskmanager_1    |      at 
>> java.lang.ClassLoader.loadClass(ClassLoader.java:351) ~[?:1.8.0_275]
>> taskmanager_1    |      ... 11 more
>> ###################################################################
>> Logfiles for 3.
>> 
>> <large-data-set-taskmanager.log>
>> <large-data-set-jobmanager.log>
>> <large-data-set-executor.log>
>> 
>>>> Dockerfile for question 2.
>>>> ####################################################################
>>>> # This image has been build based on the Dockerfile used for the flink 
>>>> image on docker hub.
>>>> # The only change I applied is that I switched to flink 1.12.0-rc1.
>>>> FROM flink:1.12.0-rc1-scala_2.12
>>>> 
>>>> # Install python
>>>> # TODO: Minimize dependencies
>>>> RUN apt-get update && apt-get install -y \
>>>>     python3 \
>>>>     python3-pip \
>>>>     python3-dev \
>>>>     zip \
>>>>   && rm -rf /var/lib/apt/lists/* \
>>>>   && ln -s /usr/bin/python3 /usr/bin/python \
>>>>   && ln -s /usr/bin/pip3 /usr/bin/pip
>>>> 
>>>> # Install pyflink
>>>> RUN wget --no-verbose 
>>>> https://dist.apache.org/repos/dist/dev/flink/flink-1.12.0-rc1/python/apache_flink-1.12.0-cp37-cp37m-manylinux1_x86_64.whl
>>>>  
>>>> <https://dist.apache.org/repos/dist/dev/flink/flink-1.12.0-rc1/python/apache_flink-1.12.0-cp37-cp37m-manylinux1_x86_64.whl>
>>>>  \
>>>>   && pip install apache_flink-1.12.0-cp37-cp37m-manylinux1_x86_64.whl \
>>>>   && rm apache_flink-1.12.0-cp37-cp37m-manylinux1_x86_64.whl
>>>> ####################################################################
>>>> Stack Trace for question 3.
>>>> ####################################################################
>>>> Caused by: java.lang.RuntimeException: Failed to close remote bundle
>>>>         at 
>>>> org.apache.flink.streaming.api.runners.python.beam.BeamPythonFunctionRunner.finishBundle(BeamPythonFunctionRunner.java:368)
>>>>         at 
>>>> org.apache.flink.streaming.api.runners.python.beam.BeamPythonFunctionRunner.flush(BeamPythonFunctionRunner.java:322)
>>>>         at 
>>>> org.apache.flink.streaming.api.operators.python.AbstractPythonFunctionOperator.invokeFinishBundle(AbstractPythonFunctionOperator.java:283)
>>>>         at 
>>>> org.apache.flink.streaming.api.operators.python.AbstractPythonFunctionOperator.checkInvokeFinishBundleByCount(AbstractPythonFunctionOperator.java:267)
>>>>         at 
>>>> org.apache.flink.table.runtime.operators.python.aggregate.arrow.batch.BatchArrowPythonGroupAggregateFunctionOperator.invokeCurrentBatch(BatchArrowPythonGroupAggregateFunctionOperator.java:64)
>>>>         at 
>>>> org.apache.flink.table.runtime.operators.python.aggregate.arrow.batch.AbstractBatchArrowPythonAggregateFunctionOperator.endInput(AbstractBatchArrowPythonAggregateFunctionOperator.java:94)
>>>>         at 
>>>> org.apache.flink.table.runtime.operators.python.aggregate.arrow.batch.BatchArrowPythonGroupAggregateFunctionOperator.endInput(BatchArrowPythonGroupAggregateFunctionOperator.java:33)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamOperatorWrapper.endOperatorInput(StreamOperatorWrapper.java:91)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamOperatorWrapper.lambda$close$0(StreamOperatorWrapper.java:127)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamTaskActionExecutor$1.runThrowing(StreamTaskActionExecutor.java:47)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamOperatorWrapper.close(StreamOperatorWrapper.java:127)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamOperatorWrapper.close(StreamOperatorWrapper.java:134)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.OperatorChain.closeOperators(OperatorChain.java:412)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamTask.afterInvoke(StreamTask.java:587)
>>>>         at 
>>>> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:549)
>>>>         at org.apache.flink.runtime.taskmanager.Task.doRun(Task.java:722)
>>>>         at org.apache.flink.runtime.taskmanager.Task.run(Task.java:547)
>>>>         at java.lang.Thread.run(Thread.java:748)
>>>> Caused by: java.util.concurrent.ExecutionException: 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.StatusRuntimeException: 
>>>> CANCELLED: cancelled before receiving half close
>>>>         at 
>>>> java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
>>>>         at 
>>>> java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1908)
>>>>         at org.apache.beam.sdk.util.MoreFutures.get(MoreFutures.java:57)
>>>>         at 
>>>> org.apache.beam.runners.fnexecution.control.SdkHarnessClient$BundleProcessor$ActiveBundle.close(SdkHarnessClient.java:458)
>>>>         at 
>>>> org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$SimpleStageBundleFactory$1.close(DefaultJobBundleFactory.java:547)
>>>>         at 
>>>> org.apache.flink.streaming.api.runners.python.beam.BeamPythonFunctionRunner.finishBundle(BeamPythonFunctionRunner.java:366)
>>>>         ... 17 more
>>>> Caused by: 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.StatusRuntimeException: 
>>>> CANCELLED: cancelled before receiving half close
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.Status.asRuntimeException(Status.java:524)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.stub.ServerCalls$StreamingServerCallHandler$StreamingServerCallListener.onCancel(ServerCalls.java:275)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.PartialForwardingServerCallListener.onCancel(PartialForwardingServerCallListener.java:40)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.ForwardingServerCallListener.onCancel(ForwardingServerCallListener.java:23)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.ForwardingServerCallListener$SimpleForwardingServerCallListener.onCancel(ForwardingServerCallListener.java:40)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.Contexts$ContextualizedServerCallListener.onCancel(Contexts.java:96)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.internal.ServerCallImpl$ServerStreamListenerImpl.closedInternal(ServerCallImpl.java:353)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.internal.ServerCallImpl$ServerStreamListenerImpl.closed(ServerCallImpl.java:341)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.internal.ServerImpl$JumpToApplicationThreadServerStreamListener$1Closed.runInContext(ServerImpl.java:867)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)
>>>>         at 
>>>> org.apache.beam.vendor.grpc.v1p26p0.io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:123)
>>>>         at 
>>>> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
>>>>         at 
>>>> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
>>>>         ... 1 more
>>>> ################################################################
>>>> Code for question 4.
>>>> ################################################################
>>>> # UDAF signature
>>>> @udaf(input_types=[DataTypes.FLOAT(), DataTypes.FLOAT()],
>>>>      result_type=DataTypes.VARCHAR(10000), func_type='pandas')
>>>> def forcast(ds_float_series, y):
>>>> 
>>>> # SQL DDL
>>>> "create table mySource (ds FLOAT, riid VARCHAR(100), y FLOAT ) with ( ... 
>>>> )"
>>>> "create table mySink (riid VARCHAR(100), yhatd VARCHAR(10000)) with ( ... 
>>>> )"
>>>> 
>>>> # SQL INSERT
>>>> "INSERT INTO mySink SELECT riid, forcast(ds, y) AS yhat FROM mySource 
>>>> GROUP BY riid"
>>>> ################################################################
>>>> 
>>>>> On 12. Nov 2020, at 12:53, Dian Fu <dian0511...@gmail.com 
>>>>> <mailto:dian0511...@gmail.com>> wrote:
>>>>> 
>>>>> Hi Niklas,
>>>>> 
>>>>> Python DataStream API will also be supported in coming release of 1.12.0 
>>>>> [1]. However, the functionalities are still limited for the time being 
>>>>> compared to the Java DataStream API, e.g. it will only support the 
>>>>> stateless operations, such as map, flat_map, etc.
>>>>> 
>>>>> [1] 
>>>>> https://ci.apache.org/projects/flink/flink-docs-master/dev/python/datastream_tutorial.html
>>>>>  
>>>>> <https://ci.apache.org/projects/flink/flink-docs-master/dev/python/datastream_tutorial.html>
>>>>>> 在 2020年11月12日,下午7:46,Niklas Wilcke <niklas.wil...@uniberg.com 
>>>>>> <mailto:niklas.wil...@uniberg.com>> 写道:
>>>>>> 
>>>>>> Hi Dian,
>>>>>> 
>>>>>> thank you very much for this valuable response. I already read about the 
>>>>>> UDAF, but I wasn't aware of the fact that it is possible to return and 
>>>>>> UNNEST an array. I will definitely have a try and hopefully this will 
>>>>>> solve my issue.
>>>>>> 
>>>>>> Another question that came up to my mind is whether PyFlink supports any 
>>>>>> other API except Table and SQL, like the Streaming and Batch API. The 
>>>>>> documentation is only covering the Table API, but I'm not sure about 
>>>>>> that. Can you maybe tell me whether the Table and SQL API is the only 
>>>>>> one supported by PyFlink?
>>>>>> 
>>>>>> Kind Regards,
>>>>>> Niklas
>>>>>> 
>>>>>>  
>>>>>> 
>>>>>>> On 11. Nov 2020, at 15:32, Dian Fu <dian0511...@gmail.com 
>>>>>>> <mailto:dian0511...@gmail.com>> wrote:
>>>>>>> 
>>>>>>> Hi Niklas,
>>>>>>> 
>>>>>>> You are correct that the input/output length of Pandas UDF must be of 
>>>>>>> the same size and that Flink will split the input data into multiple 
>>>>>>> bundles for Pandas UDF and the bundle size is non-determinstic. Both of 
>>>>>>> the above two limitations are by design and so I guess Pandas UDF could 
>>>>>>> not meet your requirements.
>>>>>>> 
>>>>>>> However, you could take a look at if the Pandas UDAF[1] which was 
>>>>>>> supported in 1.12 could meet your requirements:
>>>>>>> - As group_by only generate one record per group key just as you said, 
>>>>>>> you could declare the output type of Pandas UDAF as an array type
>>>>>>> - You need then flatten the aggregation results, e.g. using UNNEST
>>>>>>> 
>>>>>>> NOTE: Flink 1.12 is still not released. You could try the PyFlink 
>>>>>>> package of RC1[2] for 1.12.0 or build it yourself according to [3].
>>>>>>> 
>>>>>>> [1] 
>>>>>>> https://ci.apache.org/projects/flink/flink-docs-master/dev/python/table-api-users-guide/udfs/vectorized_python_udfs.html#vectorized-aggregate-functions
>>>>>>>  
>>>>>>> <https://ci.apache.org/projects/flink/flink-docs-master/dev/python/table-api-users-guide/udfs/vectorized_python_udfs.html#vectorized-aggregate-functions>
>>>>>>> [2] 
>>>>>>> https://dist.apache.org/repos/dist/dev/flink/flink-1.12.0-rc1/python/ 
>>>>>>> <https://dist.apache.org/repos/dist/dev/flink/flink-1.12.0-rc1/python/>
>>>>>>> [3] 
>>>>>>> https://ci.apache.org/projects/flink/flink-docs-master/flinkDev/building.html#build-pyflink
>>>>>>>  
>>>>>>> <https://ci.apache.org/projects/flink/flink-docs-master/flinkDev/building.html#build-pyflink>
>>>>>>> 
>>>>>>> Regards,
>>>>>>> Dian
>>>>>>> 
>>>>>>>> 在 2020年11月11日,下午9:03,Niklas Wilcke <niklas.wil...@uniberg.com 
>>>>>>>> <mailto:niklas.wil...@uniberg.com>> 写道:
>>>>>>>> 
>>>>>>>> Hi Flink Community,
>>>>>>>> 
>>>>>>>> I'm currently trying to implement a parallel machine learning job with 
>>>>>>>> Flink. The goal is to train models in parallel for independent time 
>>>>>>>> series in the same data stream. For that purpose I'm using a Python 
>>>>>>>> library, which lead me to PyFlink. Let me explain the use case a bit 
>>>>>>>> more.
>>>>>>>> I want to implement a batch job, which partitions/groups the data by a 
>>>>>>>> device identifier. After that I need to process the data for each 
>>>>>>>> device all at once. There is no way to iteratively train the model 
>>>>>>>> unfortunately. The challenge I'm facing is to guarantee that all data 
>>>>>>>> belonging to a certain device is processed in one single step. I'm 
>>>>>>>> aware of the fact that this does not scale well, but for a reasonable 
>>>>>>>> amount of input data per device it should be fine from my perspective.
>>>>>>>> I investigated a lot and I ended up using the Table API and Pandas 
>>>>>>>> UDF, which roughly fulfil my requirements, but there are the following 
>>>>>>>> limitations left, which I wanted to talk about.
>>>>>>>> 
>>>>>>>> 1. Pandas UDF takes multiple Series as input parameters, which is fine 
>>>>>>>> for my purpose, but as far as I can see there is no way to guarantee 
>>>>>>>> that the chunk of data in the Series is "complete". Flink will slice 
>>>>>>>> the Series and maybe call the UDF multiple times for each device. As 
>>>>>>>> far as I can see there are some config options like 
>>>>>>>> "python.fn-execution.arrow.batch.size" and 
>>>>>>>> "python.fn-execution.bundle.time", which might help, but I'm not sure, 
>>>>>>>> whether this is the right path to take.
>>>>>>>> 2. The length of the input Series needs to be of the same size as the 
>>>>>>>> output Series, which isn't nice for my use case. What I would like to 
>>>>>>>> do is to process n rows and emit m rows. There shouldn't be any 
>>>>>>>> dependency between the number of input rows and the number of output 
>>>>>>>> rows.
>>>>>>>> 
>>>>>>>> 3. How do I partition the data stream. The Table API offers a groupby, 
>>>>>>>> but this doesn't serve my purpose, because I don't want to aggregate 
>>>>>>>> all the grouped lines. Instead as stated above I want to emit m result 
>>>>>>>> lines per group. Are there other options using the Table API or any 
>>>>>>>> other API to do this kind of grouping. I would need something like a 
>>>>>>>> "keyBy()" from the streaming API. Maybe this can be combined? Can I 
>>>>>>>> create a separate table for each key?
>>>>>>>> 
>>>>>>>> I'm also open to ideas for a completely different approach not using 
>>>>>>>> the Table API or Pandas UDF. Any idea is welcome.
>>>>>>>> 
>>>>>>>> You can find a condensed version of the source code attached.
>>>>>>>> 
>>>>>>>> Kind Regards,
>>>>>>>> Niklas
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>> #############################################################
>>>>>>>> 
>>>>>>>> from pyflink.datastream import StreamExecutionEnvironment
>>>>>>>> from pyflink.table import StreamTableEnvironment, DataTypes
>>>>>>>> from pyflink.table.udf import udf
>>>>>>>> 
>>>>>>>> env = StreamExecutionEnvironment.get_execution_environment()
>>>>>>>> env.set_parallelism(1)
>>>>>>>> t_env = StreamTableEnvironment.create(env)
>>>>>>>> t_env.get_config().get_configuration().set_boolean("python.fn-execution.memory.managed",
>>>>>>>>  True)
>>>>>>>> 
>>>>>>>> @udf(input_types=[DataTypes.FLOAT(), DataTypes.FLOAT()],
>>>>>>>>     result_type=DataTypes.FLOAT(), udf_type='pandas')
>>>>>>>> def forcast(ds_float_series, y):
>>>>>>>> 
>>>>>>>>    # Train the model and create the forcast
>>>>>>>> 
>>>>>>>>    yhat_ts = forcast['yhat'].tail(input_size)
>>>>>>>>    return yhat_ts
>>>>>>>> 
>>>>>>>> t_env.register_function("forcast", forcast)
>>>>>>>> 
>>>>>>>> # Define sink and source here
>>>>>>>> 
>>>>>>>> t_env.execute_sql(my_source_ddl)
>>>>>>>> t_env.execute_sql(my_sink_ddl)
>>>>>>>> 
>>>>>>>> # TODO: key_by instead of filter
>>>>>>>> t_env.from_path('mySource') \
>>>>>>>>    .where("riid === 'r1i1'") \
>>>>>>>>    .select("ds, riid, y, forcast(ds, y) as yhat_90d") \
>>>>>>>>    .insert_into('mySink')
>>>>>>>> 
>>>>>>>> t_env.execute("pandas_udf_demo")
>>>>>>>> 
>>>>>>>> #############################################################
> 

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