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https://issues.apache.org/jira/browse/FLINK-4640?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephan Ewen reassigned FLINK-4640:
-----------------------------------
Assignee: Stephan Ewen
> Serialization of the initialValue of a Fold on WindowedStream fails
> -------------------------------------------------------------------
>
> Key: FLINK-4640
> URL: https://issues.apache.org/jira/browse/FLINK-4640
> Project: Flink
> Issue Type: Bug
> Components: Streaming
> Affects Versions: 1.2.0, 1.1.2
> Reporter: Fabian Hueske
> Assignee: Stephan Ewen
> Priority: Blocker
> Fix For: 1.2.0, 1.1.3
>
>
> The following program
> {code}
> DataStream<Tuple2<String, Long>> src = env.fromElements(new Tuple2<String,
> Long>("a", 1L));
> src
> .keyBy(1)
> .timeWindow(Time.minutes(5))
> .fold(TreeMultimap.<Long, String>create(), new FoldFunction<Tuple2<String,
> Long>, TreeMultimap<Long, String>>() {
> @Override
> public TreeMultimap<Long, String> fold(
> TreeMultimap<Long, String> topKSoFar,
> Tuple2<String, Long> itemCount) throws Exception
> {
> String item = itemCount.f0;
> Long count = itemCount.f1;
> topKSoFar.put(count, item);
> if (topKSoFar.keySet().size() > 10) {
> topKSoFar.removeAll(topKSoFar.keySet().first());
> }
> return topKSoFar;
> }
> });
> {code}
> throws this exception
> {quote}
> Caused by: java.lang.RuntimeException: Could not add value to folding state.
> at
> org.apache.flink.runtime.state.memory.MemFoldingState.add(MemFoldingState.java:91)
> at
> org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.processElement(WindowOperator.java:382)
> at
> org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:176)
> at
> org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:66)
> at
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:266)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:584)
> at java.lang.Thread.run(Thread.java:745)
> Caused by: java.lang.NullPointerException
> at
> com.google.common.collect.AbstractMapBasedMultimap.put(AbstractMapBasedMultimap.java:192)
> at
> com.google.common.collect.AbstractSetMultimap.put(AbstractSetMultimap.java:121)
> at com.google.common.collect.TreeMultimap.put(TreeMultimap.java:78)
> at
> org.apache.flink.streaming.examples.wordcount.WordCount$1.fold(WordCount.java:115)
> at
> org.apache.flink.streaming.examples.wordcount.WordCount$1.fold(WordCount.java:109)
> at
> org.apache.flink.runtime.state.memory.MemFoldingState.add(MemFoldingState.java:85)
> ... 6 more
> {quote}
> The exception is caused because the initial value was not correctly
> deserialized and is {{null}}.
> The user reporting this issue said that using the same {{FoldFunction}} on a
> {{KeyedStream}} (without a window) works fine.
> I tracked the problem down to the serialization of the {{StateDescriptor}},
> i.e., the {{writeObject()}} and {{readObject()}} methods. The methods use
> Flink's TypeSerializers to serialize the default value. In case of the
> {{TreeMultiMap}} this is the {{KryoSerializer}} which fails to read the
> serialized data for some reason.
> A quick workaround to solve this issue would be to check if the default value
> implements {{Serializable}} and use Java Serialization in this case. However,
> it would be good to track the root cause of this problem.
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