LIU Xiao created FLINK-11987:
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             Summary: Kafka producer occasionally throws NullpointerException
                 Key: FLINK-11987
                 URL: https://issues.apache.org/jira/browse/FLINK-11987
             Project: Flink
          Issue Type: Bug
          Components: Connectors / Kafka
    Affects Versions: 1.7.2, 1.6.4, 1.6.3
         Environment: Flink 1.6.2 (Standalone Cluster)

Oracle JDK 1.8u151

Centos 7.4
            Reporter: LIU Xiao


We are using Flink 1.6.2 in our production environment, and kafka producer 
occasionally throws NullpointerException.

We found in line 175 of 
flink/flink-connectors/flink-connector-kafka-0.11/src/main/java/org/apache/flink/streaming/connectors/kafka/FlinkKafkaProducer011.java,
 NEXT_TRANSACTIONAL_ID_HINT_DESCRIPTOR was created as a static variable.

Then in line 837, 
"context.getOperatorStateStore().getUnionListState(NEXT_TRANSACTIONAL_ID_HINT_DESCRIPTOR);"
 was called, and that leads to line 734 of 
 
flink/flink-runtime/src/main/java/org/apache/flink/runtime/state/DefaultOperatorStateBackend.java:
 "stateDescriptor.initializeSerializerUnlessSet(getExecutionConfig());"

In function initializeSerializerUnlessSet(line 283 of 
flink/flink-core/src/main/java/org/apache/flink/api/common/state/StateDescriptor.java):

if (serializer == null) {
        checkState(typeInfo != null, "no serializer and no type info");
        // instantiate the serializer
        serializer = typeInfo.createSerializer(executionConfig);
        // we can drop the type info now, no longer needed
        typeInfo  = null;
}

"serializer = typeInfo.createSerializer(executionConfig);" is the line which 
throws the exception.

We think that's because multiple subtasks of the same producer in a same 
TaskManager share a same NEXT_TRANSACTIONAL_ID_HINT_DESCRIPTOR.



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