Wesley Tanaka created BEAM-2979:
-----------------------------------
Summary: Race condition between
KafkaIO.UnboundedKafkaReader.getWatermark() and
KafkaIO.UnboundedKafkaReader.advance()
Key: BEAM-2979
URL: https://issues.apache.org/jira/browse/BEAM-2979
Project: Beam
Issue Type: Bug
Components: sdk-java-core
Affects Versions: 2.1.0, 2.0.0
Reporter: Wesley Tanaka
Assignee: Kenneth Knowles
getWatermark() looks like this:
{noformat}
@Override
public Instant getWatermark() {
if (curRecord == null) {
LOG.debug("{}: getWatermark() : no records have been read yet.", name);
return initialWatermark;
}
return source.spec.getWatermarkFn() != null
? source.spec.getWatermarkFn().apply(curRecord) : curTimestamp;
}
{noformat}
advance() has code in it that looks like this:
{noformat}
curRecord = null; // user coders below might throw.
// apply user deserializers.
// TODO: write records that can't be deserialized to a "dead-letter"
additional output.
KafkaRecord<K, V> record = new KafkaRecord<K, V>(
rawRecord.topic(),
rawRecord.partition(),
rawRecord.offset(),
consumerSpEL.getRecordTimestamp(rawRecord),
keyDeserializerInstance.deserialize(rawRecord.topic(),
rawRecord.key()),
valueDeserializerInstance.deserialize(rawRecord.topic(),
rawRecord.value()));
curTimestamp = (source.spec.getTimestampFn() == null)
? Instant.now() : source.spec.getTimestampFn().apply(record);
curRecord = record;
{noformat}
There's a race condition between these two blocks of code which is exposed at
the very least in the FlinkRunner, which calls getWatermark() periodically from
a timer.
The symptom of the race condition is a stack trace that looks like this:
{noformat}
Caused by: org.apache.flink.runtime.client.JobExecutionException: Job execution
failed.
at
org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply$mcV$sp(JobManager.scala:910)
at
org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply(JobManager.scala:853)
at
org.apache.flink.runtime.jobmanager.JobManager$$anonfun$handleMessage$1$$anonfun$applyOrElse$7.apply(JobManager.scala:853)
at
scala.concurrent.impl.Future$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: TimerException{java.lang.NullPointerException}
at
org.apache.flink.streaming.runtime.tasks.SystemProcessingTimeService$TriggerTask.run(SystemProcessingTimeService.java:220)
at
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at
java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at org.apache.beam.sdk.io.kafka.KafkaIO$Read$1.apply(KafkaIO.java:568)
at org.apache.beam.sdk.io.kafka.KafkaIO$Read$1.apply(KafkaIO.java:565)
at
org.apache.beam.sdk.io.kafka.KafkaIO$UnboundedKafkaReader.getWatermark(KafkaIO.java:1210)
at
org.apache.beam.runners.flink.translation.wrappers.streaming.io.UnboundedSourceWrapper.onProcessingTime(UnboundedSourceWrapper.java:431)
at
org.apache.flink.streaming.runtime.tasks.SystemProcessingTimeService$TriggerTask.run(SystemProcessingTimeService.java:218)
... 7 more
{noformat}
Based on inspecting the code, what is probably happening is that while
advance() is executing:
* Flink runner calls getWatermark()
* getWatermark evaluates (curRecord == null) and it is false
* advance() proceeds to set curRecord = null
* The flink runner thread calls getWatermarkFn().apply(curRecord) which passes
a null record into the custom watermark function
* If that watermark function had been set with withWatermarkFn() (as suggested
in the javadoc), then it's using the closure created in unwrapKafkaAndThen()
* That calls record.getKV() and we get the NullPointerException
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