Apache Flink fails with KryoException when serializing POJO class - apache-flink

Question

I started "playing" with Apache Flink recently. I've put together a small application to start testing the framework and so on. I'm currently running into a problem when trying to serialize a usual POJO class:
#Getter
#ToString
#EqualsAndHashCode
#NoArgsConstructor
#AllArgsConstructor
public final class Species {
private String name;
private List<String> abilities;
}
Somehow, I can tell by the stacktrace that the List type cannot be serialized, but according to Flink's documentation, that shouldn't be the case. This is the stacktrace:
2021-11-20 11:52:09,195 |- WARN in org.apache.flink.runtime.taskmanager.Task:1097 [Source: Collection Source (1/1)#0] - Source: Collection Source (1/1)#0 (4073b9fb97691d505e5a5557bf7e081b) switched from RUNNING to FAILED with failure cause: java.io.IOException: Failed to deserialize an element from the source. If you are using user-defined serialization (Value and Writable types), check the serialization functions.
Serializer is org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer#5c0e17e6
at org.apache.flink.streaming.api.functions.source.FromElementsFunction.run(FromElementsFunction.java:222)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:116)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:73)
at org.apache.flink.streaming.runtime.tasks.SourceStreamTask$LegacySourceFunctionThread.run(SourceStreamTask.java:323)
Caused by: com.esotericsoftware.kryo.KryoException: java.lang.UnsupportedOperationException
Serialization trace:
abilities (org.acme.domain.Species)
at com.esotericsoftware.kryo.serializers.ObjectField.read(ObjectField.java:125)
at com.esotericsoftware.kryo.serializers.FieldSerializer.read(FieldSerializer.java:528)
at com.esotericsoftware.kryo.Kryo.readClassAndObject(Kryo.java:761)
at org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer.deserialize(KryoSerializer.java:354)
at org.apache.flink.streaming.api.functions.source.FromElementsFunction.run(FromElementsFunction.java:220)
... 3 more
Caused by: java.lang.UnsupportedOperationException
at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:72)
at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:76)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:109)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:22)
at com.esotericsoftware.kryo.Kryo.readObject(Kryo.java:679)
at com.esotericsoftware.kryo.serializers.ObjectField.read(ObjectField.java:106)
... 7 more
Exception in thread "main" org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
at org.apache.flink.runtime.jobmaster.JobResult.toJobExecutionResult(JobResult.java:144)
at org.apache.flink.runtime.minicluster.MiniClusterJobClient.lambda$getJobExecutionResult$3(MiniClusterJobClient.java:137)
at java.base/java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:642)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2073)
at org.apache.flink.runtime.rpc.akka.AkkaInvocationHandler.lambda$invokeRpc$0(AkkaInvocationHandler.java:250)
at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:859)
at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:837)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2073)
at org.apache.flink.util.concurrent.FutureUtils.doForward(FutureUtils.java:1389)
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.lambda$null$1(ClassLoadingUtils.java:93)
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.runWithContextClassLoader(ClassLoadingUtils.java:68)
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.lambda$guardCompletionWithContextClassLoader$2(ClassLoadingUtils.java:92)
at java.base/java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:859)
at java.base/java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:837)
at java.base/java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:506)
at java.base/java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:2073)
at org.apache.flink.runtime.concurrent.akka.AkkaFutureUtils$1.onComplete(AkkaFutureUtils.java:47)
at akka.dispatch.OnComplete.internal(Future.scala:300)
at akka.dispatch.OnComplete.internal(Future.scala:297)
at akka.dispatch.japi$CallbackBridge.apply(Future.scala:224)
at akka.dispatch.japi$CallbackBridge.apply(Future.scala:221)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
at org.apache.flink.runtime.concurrent.akka.AkkaFutureUtils$DirectExecutionContext.execute(AkkaFutureUtils.java:65)
at scala.concurrent.impl.CallbackRunnable.executeWithValue(Promise.scala:68)
at scala.concurrent.impl.Promise$DefaultPromise.$anonfun$tryComplete$1(Promise.scala:284)
at scala.concurrent.impl.Promise$DefaultPromise.$anonfun$tryComplete$1$adapted(Promise.scala:284)
at scala.concurrent.impl.Promise$DefaultPromise.tryComplete(Promise.scala:284)
at akka.pattern.PromiseActorRef.$bang(AskSupport.scala:621)
at akka.pattern.PipeToSupport$PipeableFuture$$anonfun$pipeTo$1.applyOrElse(PipeToSupport.scala:24)
at akka.pattern.PipeToSupport$PipeableFuture$$anonfun$pipeTo$1.applyOrElse(PipeToSupport.scala:23)
at scala.concurrent.Future.$anonfun$andThen$1(Future.scala:532)
at scala.concurrent.impl.Promise.liftedTree1$1(Promise.scala:29)
at scala.concurrent.impl.Promise.$anonfun$transform$1(Promise.scala:29)
at scala.concurrent.impl.CallbackRunnable.run(Promise.scala:60)
at akka.dispatch.BatchingExecutor$AbstractBatch.processBatch(BatchingExecutor.scala:63)
at akka.dispatch.BatchingExecutor$BlockableBatch.$anonfun$run$1(BatchingExecutor.scala:100)
at scala.runtime.java8.JFunction0$mcV$sp.apply(JFunction0$mcV$sp.java:12)
at scala.concurrent.BlockContext$.withBlockContext(BlockContext.scala:81)
at akka.dispatch.BatchingExecutor$BlockableBatch.run(BatchingExecutor.scala:100)
at akka.dispatch.TaskInvocation.run(AbstractDispatcher.scala:49)
at akka.dispatch.ForkJoinExecutorConfigurator$AkkaForkJoinTask.exec(ForkJoinExecutorConfigurator.scala:48)
at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)
Caused by: org.apache.flink.runtime.JobException: Recovery is suppressed by NoRestartBackoffTimeStrategy
at org.apache.flink.runtime.executiongraph.failover.flip1.ExecutionFailureHandler.handleFailure(ExecutionFailureHandler.java:138)
at org.apache.flink.runtime.executiongraph.failover.flip1.ExecutionFailureHandler.getFailureHandlingResult(ExecutionFailureHandler.java:82)
at org.apache.flink.runtime.scheduler.DefaultScheduler.handleTaskFailure(DefaultScheduler.java:228)
at org.apache.flink.runtime.scheduler.DefaultScheduler.maybeHandleTaskFailure(DefaultScheduler.java:218)
at org.apache.flink.runtime.scheduler.DefaultScheduler.updateTaskExecutionStateInternal(DefaultScheduler.java:209)
at org.apache.flink.runtime.scheduler.SchedulerBase.updateTaskExecutionState(SchedulerBase.java:679)
at org.apache.flink.runtime.scheduler.SchedulerNG.updateTaskExecutionState(SchedulerNG.java:79)
at org.apache.flink.runtime.jobmaster.JobMaster.updateTaskExecutionState(JobMaster.java:444)
at jdk.internal.reflect.GeneratedMethodAccessor11.invoke(Unknown Source)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.lambda$handleRpcInvocation$1(AkkaRpcActor.java:316)
at org.apache.flink.runtime.concurrent.akka.ClassLoadingUtils.runWithContextClassLoader(ClassLoadingUtils.java:83)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleRpcInvocation(AkkaRpcActor.java:314)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleRpcMessage(AkkaRpcActor.java:217)
at org.apache.flink.runtime.rpc.akka.FencedAkkaRpcActor.handleRpcMessage(FencedAkkaRpcActor.java:78)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleMessage(AkkaRpcActor.java:163)
at akka.japi.pf.UnitCaseStatement.apply(CaseStatements.scala:24)
at akka.japi.pf.UnitCaseStatement.apply(CaseStatements.scala:20)
at scala.PartialFunction.applyOrElse(PartialFunction.scala:123)
at scala.PartialFunction.applyOrElse$(PartialFunction.scala:122)
at akka.japi.pf.UnitCaseStatement.applyOrElse(CaseStatements.scala:20)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:171)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:172)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:172)
at akka.actor.Actor.aroundReceive(Actor.scala:537)
at akka.actor.Actor.aroundReceive$(Actor.scala:535)
at akka.actor.AbstractActor.aroundReceive(AbstractActor.scala:220)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:580)
at akka.actor.ActorCell.invoke(ActorCell.scala:548)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:270)
at akka.dispatch.Mailbox.run(Mailbox.scala:231)
at akka.dispatch.Mailbox.exec(Mailbox.scala:243)
... 5 more
Caused by: java.io.IOException: Failed to deserialize an element from the source. If you are using user-defined serialization (Value and Writable types), check the serialization functions.
Serializer is org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer#5c0e17e6
at org.apache.flink.streaming.api.functions.source.FromElementsFunction.run(FromElementsFunction.java:222)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:116)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:73)
at org.apache.flink.streaming.runtime.tasks.SourceStreamTask$LegacySourceFunctionThread.run(SourceStreamTask.java:323)
Caused by: com.esotericsoftware.kryo.KryoException: java.lang.UnsupportedOperationException
Serialization trace:
abilities (org.acme.domain.Species)
at com.esotericsoftware.kryo.serializers.ObjectField.read(ObjectField.java:125)
at com.esotericsoftware.kryo.serializers.FieldSerializer.read(FieldSerializer.java:528)
at com.esotericsoftware.kryo.Kryo.readClassAndObject(Kryo.java:761)
at org.apache.flink.api.java.typeutils.runtime.kryo.KryoSerializer.deserialize(KryoSerializer.java:354)
at org.apache.flink.streaming.api.functions.source.FromElementsFunction.run(FromElementsFunction.java:220)
... 3 more
Caused by: java.lang.UnsupportedOperationException
at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:72)
at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:76)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:109)
at com.esotericsoftware.kryo.serializers.CollectionSerializer.read(CollectionSerializer.java:22)
at com.esotericsoftware.kryo.Kryo.readObject(Kryo.java:679)
at com.esotericsoftware.kryo.serializers.ObjectField.read(ObjectField.java:106)
... 7 more
Process finished with exit code 1
I've tried adding enableForceKyro to StreamExecutionEnvironment.getExecutionEnvironment().getCOnfig, but didn't change anything.
What am I missing here? I'm using Apache Flink 1.14.0 with Java (Eclipse Temurin) 11.x.

Answer 1

Since the issue is with Kryo serialization, you can register your own custom Kryo serializers. But in my experience this hasn't worked all that well for reasons I don't completely understand (not always used). Plus Kryo serialization is going to be much slower than creating a POJO that Flink can serialize using built-in support. So add setters for every field, verify nothing gets logged about class Species missing something that qualifies it for fast serialization, and you should be all set.