【发布时间】：2016-12-30 09:49:03
【问题描述】：
我正在尝试使用 Kafka Streams 0.10.1 在 Scala 中创建一个简单的聚合示例，尽管我似乎因简单的“计数”聚合而失败（使用 Kafka 控制台生产者）。有了这样的代码：
val inputStream: KStream[String, String] = builder.stream("inputTopic")
inputStream
.map(new KeyValueMapper[String, String, KeyValue[String, String]] {
override def apply(k: String, v: String): KeyValue[String, String] = {
new KeyValue[String, String](v, v)
}
})
.groupByKey()
.count(TimeWindows.of(10000L), "count-test-1")
.toStream()
.to("outputTopic")
它失败并显示“无法刷新状态存储 count-test-1”，我在帖子末尾包含了完整的堆栈跟踪。另一方面，如果我使用 print() 而不是 to() 它就像一个魅力，将结果打印到控制台/终端：
[KTABLE-TOSTREAM-0000000013]: [aa@1483089460000] , 1
[KTABLE-TOSTREAM-0000000013]: [bb@1483089460000] , 1
[KTABLE-TOSTREAM-0000000013]: [cc@1483089460000] , 2
[KTABLE-TOSTREAM-0000000013]: [dd@1483089460000] , 3
[KTABLE-TOSTREAM-0000000013]: [ee@1483089460000] , 4
有谁知道这种行为的原因可能是什么？
仅供参考，我使用的操作系统是 Windows 10 作为主机（也通过 IntelliJ 运行 Scala 应用程序）和用于 Kafka（在 Docker 容器中）和生产者/消费者应用程序的 Ubuntu 16.04 VM。但是，我可以确认，在 Ubuntu VM 上运行应用程序时也会遇到此问题。
非常感谢您的帮助，感谢您的任何见解:-)
完整的堆栈跟踪：
2016-12-30 08:57:43 INFO StreamThread:573 - stream-thread [StreamThread-1] Committing task 2_0
2016-12-30 08:57:43 ERROR StreamThread:582 - stream-thread [StreamThread-1] Failed to commit StreamTask 2_0 state:
org.apache.kafka.streams.errors.ProcessorStateException: task [2_0] Failed to flush state store count-test-1
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:331)
at org.apache.kafka.streams.processor.internals.StreamTask.commit(StreamTask.java:275)
at org.apache.kafka.streams.processor.internals.StreamThread.commitOne(StreamThread.java:576)
at org.apache.kafka.streams.processor.internals.StreamThread.commitAll(StreamThread.java:562)
at org.apache.kafka.streams.processor.internals.StreamThread.maybeCommit(StreamThread.java:538)
at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:456)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:242)
Caused by: java.lang.ClassCastException: org.apache.kafka.streams.kstream.Windowed cannot be cast to java.lang.String
at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:24)
at org.apache.kafka.streams.processor.internals.RecordCollector.send(RecordCollector.java:72)
at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:72)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.KStreamMapValues$KStreamMapProcessor.process(KStreamMapValues.java:42)
at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.ForwardingCacheFlushListener.apply(ForwardingCacheFlushListener.java:35)
at org.apache.kafka.streams.state.internals.CachingWindowStore.maybeForward(CachingWindowStore.java:103)
at org.apache.kafka.streams.state.internals.CachingWindowStore.access$200(CachingWindowStore.java:34)
at org.apache.kafka.streams.state.internals.CachingWindowStore$1.apply(CachingWindowStore.java:86)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:117)
at org.apache.kafka.streams.state.internals.ThreadCache.flush(ThreadCache.java:100)
at org.apache.kafka.streams.state.internals.CachingWindowStore.flush(CachingWindowStore.java:118)
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:329)
... 6 more
2016-12-30 08:57:43 INFO StreamThread:268 - stream-thread [StreamThread-1] Shutting down
2016-12-30 08:57:43 INFO StreamThread:358 - stream-thread [StreamThread-1] Committing consumer offsets of task 0_0
2016-12-30 08:57:43 INFO StreamThread:358 - stream-thread [StreamThread-1] Committing consumer offsets of task 1_0
2016-12-30 08:57:43 INFO StreamThread:358 - stream-thread [StreamThread-1] Committing consumer offsets of task 2_0
2016-12-30 08:57:43 INFO StreamThread:751 - stream-thread [StreamThread-1] Closing a task 0_0
2016-12-30 08:57:43 INFO StreamThread:751 - stream-thread [StreamThread-1] Closing a task 1_0
2016-12-30 08:57:43 INFO StreamThread:751 - stream-thread [StreamThread-1] Closing a task 2_0
2016-12-30 08:57:43 INFO StreamThread:368 - stream-thread [StreamThread-1] Flushing state stores of task 0_0
2016-12-30 08:57:43 INFO StreamThread:368 - stream-thread [StreamThread-1] Flushing state stores of task 1_0
2016-12-30 08:57:43 INFO StreamThread:368 - stream-thread [StreamThread-1] Flushing state stores of task 2_0
2016-12-30 08:57:43 ERROR StreamThread:330 - stream-thread [StreamThread-1] Failed while executing StreamTask 2_0 duet to flush state:
org.apache.kafka.streams.errors.ProcessorStateException: task [2_0] Failed to flush state store count-test-1
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:331)
at org.apache.kafka.streams.processor.internals.AbstractTask.flushState(AbstractTask.java:180)
at org.apache.kafka.streams.processor.internals.StreamThread$4.apply(StreamThread.java:369)
at org.apache.kafka.streams.processor.internals.StreamThread.performOnAllTasks(StreamThread.java:328)
at org.apache.kafka.streams.processor.internals.StreamThread.flushAllState(StreamThread.java:365)
at org.apache.kafka.streams.processor.internals.StreamThread.shutdownTasksAndState(StreamThread.java:301)
at org.apache.kafka.streams.processor.internals.StreamThread.shutdown(StreamThread.java:269)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:252)
Caused by: java.lang.ClassCastException: org.apache.kafka.streams.kstream.Windowed cannot be cast to java.lang.String
at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:24)
at org.apache.kafka.streams.processor.internals.RecordCollector.send(RecordCollector.java:72)
at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:72)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.KStreamMapValues$KStreamMapProcessor.process(KStreamMapValues.java:42)
at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.ForwardingCacheFlushListener.apply(ForwardingCacheFlushListener.java:35)
at org.apache.kafka.streams.state.internals.CachingWindowStore.maybeForward(CachingWindowStore.java:103)
at org.apache.kafka.streams.state.internals.CachingWindowStore.access$200(CachingWindowStore.java:34)
at org.apache.kafka.streams.state.internals.CachingWindowStore$1.apply(CachingWindowStore.java:86)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:117)
at org.apache.kafka.streams.state.internals.ThreadCache.flush(ThreadCache.java:100)
at org.apache.kafka.streams.state.internals.CachingWindowStore.flush(CachingWindowStore.java:118)
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:329)
... 7 more
2016-12-30 08:57:43 INFO StreamThread:347 - stream-thread [StreamThread-1] Closing the state manager of task 0_0
2016-12-30 08:57:43 INFO StreamThread:347 - stream-thread [StreamThread-1] Closing the state manager of task 1_0
2016-12-30 08:57:43 INFO StreamThread:347 - stream-thread [StreamThread-1] Closing the state manager of task 2_0
2016-12-30 08:57:43 ERROR StreamThread:330 - stream-thread [StreamThread-1] Failed while executing StreamTask 2_0 duet to close state manager:
org.apache.kafka.streams.errors.ProcessorStateException: task [2_0] Failed to close state store count-test-1
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.close(ProcessorStateManager.java:351)
at org.apache.kafka.streams.processor.internals.AbstractTask.closeStateManager(AbstractTask.java:120)
at org.apache.kafka.streams.processor.internals.StreamThread$2.apply(StreamThread.java:348)
at org.apache.kafka.streams.processor.internals.StreamThread.performOnAllTasks(StreamThread.java:328)
at org.apache.kafka.streams.processor.internals.StreamThread.closeAllStateManagers(StreamThread.java:344)
at org.apache.kafka.streams.processor.internals.StreamThread.shutdownTasksAndState(StreamThread.java:305)
at org.apache.kafka.streams.processor.internals.StreamThread.shutdown(StreamThread.java:269)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:252)
Caused by: java.lang.ClassCastException: org.apache.kafka.streams.kstream.Windowed cannot be cast to java.lang.String
at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:24)
at org.apache.kafka.streams.processor.internals.RecordCollector.send(RecordCollector.java:72)
at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:72)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.KStreamMapValues$KStreamMapProcessor.process(KStreamMapValues.java:42)
at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.ForwardingCacheFlushListener.apply(ForwardingCacheFlushListener.java:35)
at org.apache.kafka.streams.state.internals.CachingWindowStore.maybeForward(CachingWindowStore.java:103)
at org.apache.kafka.streams.state.internals.CachingWindowStore.access$200(CachingWindowStore.java:34)
at org.apache.kafka.streams.state.internals.CachingWindowStore$1.apply(CachingWindowStore.java:86)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:117)
at org.apache.kafka.streams.state.internals.ThreadCache.flush(ThreadCache.java:100)
at org.apache.kafka.streams.state.internals.CachingWindowStore.flush(CachingWindowStore.java:118)
at org.apache.kafka.streams.state.internals.CachingWindowStore.close(CachingWindowStore.java:124)
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.close(ProcessorStateManager.java:349)
... 7 more
2016-12-30 08:57:43 INFO KafkaProducer:685 - Closing the Kafka producer with timeoutMillis = 9223372036854775807 ms.
2016-12-30 08:57:43 INFO StreamThread:725 - stream-thread [StreamThread-1] Removing all active tasks [[0_0, 1_0, 2_0]]
2016-12-30 08:57:43 INFO StreamThread:740 - stream-thread [StreamThread-1] Removing all standby tasks [[]]
2016-12-30 08:57:43 INFO StreamThread:292 - stream-thread [StreamThread-1] Stream thread shutdown complete
Exception in thread "StreamThread-1" org.apache.kafka.streams.errors.ProcessorStateException: task [2_0] Failed to flush state store count-test-1
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:331)
at org.apache.kafka.streams.processor.internals.StreamTask.commit(StreamTask.java:275)
at org.apache.kafka.streams.processor.internals.StreamThread.commitOne(StreamThread.java:576)
at org.apache.kafka.streams.processor.internals.StreamThread.commitAll(StreamThread.java:562)
at org.apache.kafka.streams.processor.internals.StreamThread.maybeCommit(StreamThread.java:538)
at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:456)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:242)
Caused by: java.lang.ClassCastException: org.apache.kafka.streams.kstream.Windowed cannot be cast to java.lang.String
at org.apache.kafka.common.serialization.StringSerializer.serialize(StringSerializer.java:24)
at org.apache.kafka.streams.processor.internals.RecordCollector.send(RecordCollector.java:72)
at org.apache.kafka.streams.processor.internals.SinkNode.process(SinkNode.java:72)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.KStreamMapValues$KStreamMapProcessor.process(KStreamMapValues.java:42)
at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:82)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:204)
at org.apache.kafka.streams.kstream.internals.ForwardingCacheFlushListener.apply(ForwardingCacheFlushListener.java:35)
at org.apache.kafka.streams.state.internals.CachingWindowStore.maybeForward(CachingWindowStore.java:103)
at org.apache.kafka.streams.state.internals.CachingWindowStore.access$200(CachingWindowStore.java:34)
at org.apache.kafka.streams.state.internals.CachingWindowStore$1.apply(CachingWindowStore.java:86)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:117)
at org.apache.kafka.streams.state.internals.ThreadCache.flush(ThreadCache.java:100)
at org.apache.kafka.streams.state.internals.CachingWindowStore.flush(CachingWindowStore.java:118)
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:329)
... 6 more
2016-12-30 08:57:43 INFO KafkaStreams:237 - Stopped Kafka Stream process
【问题讨论】：
标签： scala apache-kafka-streams