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From "Erik van Oosten (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-5633) ClassCastException: X cannot be cast to X when re-submitting a job.
Date Tue, 07 Nov 2017 09:04:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-5633?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16241701#comment-16241701
] 

Erik van Oosten commented on FLINK-5633:
----------------------------------------

[~StephanEwen] We need to process 130K msg/s, I guess that can be called often :) . Our process
is CPU bound and parsing Avro is ±15% of that. Any improvement means we can run with fewer
machines.

For every message we create a new SpecificDatumReader. If I follow the code correctly that
should _not_ give a large overhead. The Schema instances we pass to it _are_ cached.

Then we call {SpecificDatumReader.read}} to parse each Avro message. In that call you eventually
end up in {{SpecificData.newInstance}} to create a new instance of the target class. The constructor
of that class is looked up in a cache. That cache is declared as {{static}}. I do not understand
how instantiating a new {{SpecificData}} for every call to {{read}} helps because it would
still use the same cache. The code I pasted above also uses a constructor cache but the cache
is not {{static}}. Reversing the class loader order should also work.

> ClassCastException: X cannot be cast to X when re-submitting a job.
> -------------------------------------------------------------------
>
>                 Key: FLINK-5633
>                 URL: https://issues.apache.org/jira/browse/FLINK-5633
>             Project: Flink
>          Issue Type: Bug
>          Components: Job-Submission, YARN
>    Affects Versions: 1.1.4
>            Reporter: Giuliano Caliari
>            Priority: Minor
>
> I’m running a job on my local cluster and the first time I submit the job everything
works but whenever I cancel and re-submit the same job it fails with:
> {quote}
> org.apache.flink.client.program.ProgramInvocationException: The program execution failed:
Job execution failed.
> 	at org.apache.flink.client.program.ClusterClient.run(ClusterClient.java:427)
> 	at org.apache.flink.client.program.StandaloneClusterClient.submitJob(StandaloneClusterClient.java:101)
> 	at org.apache.flink.client.program.ClusterClient.run(ClusterClient.java:400)
> 	at org.apache.flink.streaming.api.environment.StreamContextEnvironment.execute(StreamContextEnvironment.java:66)
> 	at org.apache.flink.streaming.api.scala.StreamExecutionEnvironment.execute(StreamExecutionEnvironment.scala:634)
> 	at au.com.my.package.pTraitor.OneTrait.execute(Traitor.scala:147)
> 	at au.com.my.package.pTraitor.TraitorAppOneTrait$.delayedEndpoint$au$com$my$package$pTraitor$TraitorAppOneTrait$1(TraitorApp.scala:22)
> 	at au.com.my.package.pTraitor.TraitorAppOneTrait$delayedInit$body.apply(TraitorApp.scala:21)
> 	at scala.Function0$class.apply$mcV$sp(Function0.scala:34)
> 	at scala.runtime.AbstractFunction0.apply$mcV$sp(AbstractFunction0.scala:12)
> 	at scala.App$$anonfun$main$1.apply(App.scala:76)
> 	at scala.App$$anonfun$main$1.apply(App.scala:76)
> 	at scala.collection.immutable.List.foreach(List.scala:381)
> 	at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:35)
> 	at scala.App$class.main(App.scala:76)
> 	at au.com.my.package.pTraitor.TraitorAppOneTrait$.main(TraitorApp.scala:21)
> 	at au.com.my.package.pTraitor.TraitorAppOneTrait.main(TraitorApp.scala)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> 	at java.lang.reflect.Method.invoke(Method.java:498)
> 	at org.apache.flink.client.program.PackagedProgram.callMainMethod(PackagedProgram.java:528)
> 	at org.apache.flink.client.program.PackagedProgram.invokeInteractiveModeForExecution(PackagedProgram.java:419)
> 	at org.apache.flink.client.program.ClusterClient.run(ClusterClient.java:339)
> 	at org.apache.flink.client.CliFrontend.executeProgram(CliFrontend.java:831)
> 	at org.apache.flink.client.CliFrontend.run(CliFrontend.java:256)
> 	at org.apache.flink.client.CliFrontend.parseParameters(CliFrontend.java:1073)
> 	at org.apache.flink.client.CliFrontend$2.call(CliFrontend.java:1120)
> 	at org.apache.flink.client.CliFrontend$2.call(CliFrontend.java:1117)
> 	at org.apache.flink.runtime.security.NoOpSecurityContext.runSecured(NoOpSecurityContext.java:29)
> 	at org.apache.flink.client.CliFrontend.main(CliFrontend.java:1116)
> Caused by: org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
> 	at org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$6.apply$mcV$sp(JobManager.scala:900)
> 	at org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$6.apply(JobManager.scala:843)
> 	at org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$6.apply(JobManager.scala:843)
> 	at scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future.scala:24)
> 	at scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
> 	at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:40)
> 	at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(AbstractDispatcher.scala:397)
> 	at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
> 	at scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
> 	at scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
> 	at scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
> Caused by: java.lang.RuntimeException: Could not forward element to next operator
> 	at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:415)
> 	at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:397)
> 	at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:749)
> 	at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:727)
> 	at org.apache.flink.streaming.api.operators.StreamSourceContexts$ManualWatermarkContext.collectWithTimestamp(StreamSourceContexts.java:272)
> 	at org.apache.flink.streaming.connectors.kafka.internals.AbstractFetcher.emitRecordWithTimestamp(AbstractFetcher.java:261)
> 	at org.apache.flink.streaming.connectors.kafka.internal.Kafka010Fetcher.emitRecord(Kafka010Fetcher.java:88)
> 	at org.apache.flink.streaming.connectors.kafka.internal.Kafka09Fetcher.runFetchLoop(Kafka09Fetcher.java:157)
> 	at org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumerBase.run(FlinkKafkaConsumerBase.java:255)
> 	at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:78)
> 	at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:55)
> 	at org.apache.flink.streaming.runtime.tasks.SourceStreamTask.run(SourceStreamTask.java:56)
> 	at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:269)
> 	at org.apache.flink.runtime.taskmanager.Task.run(Task.java:654)
> 	at java.lang.Thread.run(Thread.java:745)
> Caused by: java.lang.ClassCastException: au.com.my.package.schema.p.WowTransaction cannot
be cast to au.com.my.package.schema.p.WowTransaction
> 	at au.com.my.package.pTraitor.OneTrait$$anonfun$execute$4.apply(Traitor.scala:132)
> 	at org.apache.flink.streaming.api.scala.DataStream$$anon$1.extractAscendingTimestamp(DataStream.scala:763)
> 	at org.apache.flink.streaming.api.functions.timestamps.AscendingTimestampExtractor.extractTimestamp(AscendingTimestampExtractor.java:72)
> 	at org.apache.flink.streaming.runtime.operators.TimestampsAndPeriodicWatermarksOperator.processElement(TimestampsAndPeriodicWatermarksOperator.java:65)
> 	at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:412)
> 	... 14 more
> {quote}
> This happens on versions 1.1.4 and 1.2
> Here's a great description of the problem, provided by Yury Ruchin:
> {quote}
> In YARN setup there are several sources where classes are loaded from: Flink lib directory,
YARN lib directories, user code. The first two sources are handled by system classloader,
the last one is loaded by FlinkUserCodeClassLoader.
> My streaming job parses Avro-encoded data using SpecificRecord facility. In essence,
the job looks like this: Source -> Avro parser (Map) -> Sink. Parallelism is 1. Job
operates inside a long-lived YARN session. I have a subclass of SpecificRecord, say it's name
is MySpecificRecord. From class loading perspective, Avro library classes, including the SpecificRecord,
are loaded by system class loader from YARN lib dir - such classes are shared across different
Flink tasks within task manager. On the other side, MySpecificRecord is in the job fat jar,
so it gets loaded by FlinkUserCodeClassLoader. Upon every job restart, task gets a new FlinkUserCodeClassLoader
instance, so classes from user code are confined to a task instance.
> Simply put, the parsing itself looks like this:
> val bean = new SpecificDatumReader[MySpecificRecord](MySpecificRecord.getClassSchema).read(...)
> Now, the scenario:
> 1. I start my job. Parsing is initiated, so the SpecificDatumReader and SpecificData
get loaded by system classloader. A new FlinkUserCodeClassloader is instantiated, let's denote
its instance as "A". MySpecificRecord then gets loaded by A.
> 2. SpecificData gets a singleton SpecificData.INSTANCE that holds a cache that maps some
string key derived from Avro schema to the implementing class. So during parsing I get MySpecificRecord
(A) cached there.
> 3. I stop the job and re-submit it. The JVM process is the same, so all standard Avro
classes, including SpecificData, remain loaded. A new task instance is created and gets a
new FlinkUserCodeClassLoader instance, let's name it "B". A new MySpecificRecord class incarnation
is loaded by B. From JVM standpoint MySpecificRecord (B) is different from MySpecificRecord
(A), even though their bytecode is identical.
> 4. The job starts parsing again. SpecificDatumReader consults SpecificData.INSTANCE's
cache for any stashed classes and finds MySpecificRecord (A) there.
> 5. SpecificDatumReader uses the cached MySpecificRecord (A) to instantiate a bean for
filling the parsed data in.
> 6. SpecificDatumReader hands the filled instance of MySpecificRecord (A) back to job.
> 7. Job tries to cast MySpecificRecord (A) to MySpecificRecord (B).
> 8. ClassCastException :^(
> I fixed the issue by not using the SpecificData.INSTANCE singleton (even though this
is considered a common and expected practice). I feed every parser a new instance of SpecificData.
This way the class cache is confined to a parser instance and gets recycled along with it.
> {quote}
> A discussion the the error can be found at:
> http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/How-to-get-help-on-ClassCastException-when-re-submitting-a-job-td10972.html



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