Flink strange “Cannot Serialize operator object class …CoBroadcastWithNonKeyedOperator” error

Question

I am trying to set up a project using BroadcastState, but for some reason I am getting this error when I try to run it:

org.apache.flink.streaming.runtime.tasks.StreamTaskException: Cannot serialize operator object class org.apache.flink.streaming.api.operators.co.CoBroadcastWithNonKeyedOperator.

I am not sure why it is throwing it. The objects passed into and output by it (SampleInput and Token) are very simple avro generated pojos with two or three fields and I tried just leaving the BroadcastProcessFunction's methods blank to cut out anything I could be setting to make in unable to be serialized, but still getting the error. Here is the relevant part of the code:

//Sideoutput that error strings will be written to
    OutputTag<String> sideOutputTag = new OutputTag<String>("side-output") {};

    //<Setup for broadcast state>
    StateTtlConfig ttlConfig = StateTtlConfig
            .newBuilder(Time.seconds(1))
            .setUpdateType(StateTtlConfig.UpdateType.OnCreateAndWrite)
            .setStateVisibility(StateTtlConfig.StateVisibility.NeverReturnExpired)
            .cleanupFullSnapshot()
            .build();

    final MapStateDescriptor<String, Token> ruleStateDescriptor = new MapStateDescriptor<>(
            "oathTokens",
            BasicTypeInfo.STRING_TYPE_INFO,
            AvroTypeInfo.of(new TypeHint<Token>() {}));
    ruleStateDescriptor.enableTimeToLive(ttlConfig);

    DataStream<Token> tokenObjectStream = tokenSourceStream.process(new JsonToTokenProcessFunction(sideOutputTag))
            .startNewChain()
            .uid("tokenObjectStream")
            .name("tokenObjectStream");

    BroadcastStream<Token> ruleBroadcastStream = tokenObjectStream.broadcast(ruleStateDescriptor);
    //</Config for broadcast state>


    //<Main Data Input Stream>
    DataStream<SampleInput> jsonToSampleInput = kafkaStream.process(new JsonToPojoProcessFunction(sideOutputTag))
            .startNewChain()
            .uid("sampleInputStream")
            .name("sampleInputStream");

    BroadcastConnectedStream<SampleInput, Token> broadcastConnectedStream = jsonToSampleInput.connect(ruleBroadcastStream);

    DataStream<SampleInput> matchedBroadcastStream = broadcastConnectedStream.process(new BroadcastProcessFunction<SampleInput, Token, SampleInput>() {

        @Override
        public void processElement(SampleInput sampleInput, ReadOnlyContext readOnlyContext, Collector<SampleInput> collector) throws Exception {

        }

        @Override
        public void processBroadcastElement(Token token, Context context, Collector<SampleInput> collector) throws Exception {

        }
    });

Any help would be greatly appreciated. I am sure I am just overlooking something. Thanks!

Answer 1

Turns out the ttlConfig object is what wasn't serializable. Removing it resolved the issue.