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https://issues.apache.org/jira/browse/FLINK-10353?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16676695#comment-16676695
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ASF GitHub Bot commented on FLINK-10353:
----------------------------------------

StefanRRichter commented on issue #7010: [FLINK-10353][kafka] Support change of 
transactional semantics in Kaf…
URL: https://github.com/apache/flink/pull/7010#issuecomment-436235901
 
 
   Addressed the comments. Please have another look.

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> Restoring a KafkaProducer with Semantic.EXACTLY_ONCE from a savepoint written 
> with Semantic.AT_LEAST_ONCE fails with NPE
> ------------------------------------------------------------------------------------------------------------------------
>
>                 Key: FLINK-10353
>                 URL: https://issues.apache.org/jira/browse/FLINK-10353
>             Project: Flink
>          Issue Type: Improvement
>          Components: Kafka Connector
>    Affects Versions: 1.5.3, 1.6.0
>            Reporter: Konstantin Knauf
>            Assignee: Stefan Richter
>            Priority: Critical
>              Labels: pull-request-available
>
> If a KafkaProducer with {{Semantic.EXACTLY_ONCE}} is restored from a 
> savepoint written with {{Semantic.AT_LEAST_ONCE}} the job fails on restore 
> with the NPE below. This makes it impossible to upgrade an AT_LEAST_ONCE 
> pipeline to an EXACTL_ONCE pipeline statefully.
> {quote}
> java.lang.NullPointerException
>       at java.util.Hashtable.put(Hashtable.java:460)
>       at 
> org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer011.initTransactionalProducer(FlinkKafkaProducer011.java:955)
>       at 
> org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer011.recoverAndCommit(FlinkKafkaProducer011.java:733)
>       at 
> org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer011.recoverAndCommit(FlinkKafkaProducer011.java:93)
>       at 
> org.apache.flink.streaming.api.functions.sink.TwoPhaseCommitSinkFunction.recoverAndCommitInternal(TwoPhaseCommitSinkFunction.java:373)
>       at 
> org.apache.flink.streaming.api.functions.sink.TwoPhaseCommitSinkFunction.initializeState(TwoPhaseCommitSinkFunction.java:333)
>       at 
> org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer011.initializeState(FlinkKafkaProducer011.java:867)
>       at 
> org.apache.flink.streaming.util.functions.StreamingFunctionUtils.tryRestoreFunction(StreamingFunctionUtils.java:178)
>       at 
> org.apache.flink.streaming.util.functions.StreamingFunctionUtils.restoreFunctionState(StreamingFunctionUtils.java:160)
>       at 
> org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.initializeState(AbstractUdfStreamOperator.java:96)
>       at 
> org.apache.flink.streaming.api.operators.AbstractStreamOperator.initializeState(AbstractStreamOperator.java:254)
>       at 
> org.apache.flink.streaming.runtime.tasks.StreamTask.initializeState(StreamTask.java:738)
>       at 
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:289)
>       at org.apache.flink.runtime.taskmanager.Task.run(Task.java:711)
>       at java.lang.Thread.run(Thread.java:748){quote}
> The reason is, that for {{Semantic.AT_LEAST_ONCE}} the snapshotted state of 
> the {{TwoPhaseCommitFunction}} is of the form 
> "TransactionHolder\{handle=KafkaTransactionState [transactionalId=null, 
> producerId=-1, epoch=-1], transactionStartTime=1537175471175}".



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