Manu Zhang created FLINK-4862:
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Summary: NPE on EventTimeSessionWindows with ContinuousEventTimeTrigger
Key: FLINK-4862
URL:
https://issues.apache.org/jira/browse/FLINK-4862 Project: Flink
Issue Type: Bug
Components: Streaming, Windowing Operators
Reporter: Manu Zhang
h3. what's the error ?
The following NPE error is thrown when EventTimeSessionWindows with ContinuousEventTimeTrigger is used.
{code}
Caused by: java.lang.NullPointerException
at org.apache.flink.streaming.api.windowing.triggers.ContinuousEventTimeTrigger.clear(ContinuousEventTimeTrigger.java:91)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$Context.clear(WindowOperator.java:768)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:310)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator$2.merge(WindowOperator.java:297)
at org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSet.addWindow(MergingWindowSet.java:196)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.processElement(WindowOperator.java:297)
at org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:183)
at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:66)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:271)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:609)
at java.lang.Thread.run(Thread.java:745)
{code}
h3. how to reproduce ?
use {{ContinuousEventTimeTrigger}} instead of the default {{EventTimeTrigger}} in [SessionWindowing |
https://github.com/apache/flink/blob/master/flink-examples/flink-examples-streaming/src/main/java/org/apache/flink/streaming/examples/windowing/SessionWindowing.java#L84] example.
h3. what's the cause ?
When two session windows are being merged, the states of the two {{ContinuousEventTimeTrigger}} are merged as well and the new namespace is the merged window. Later when the context tries to delete {{Timer}} from the old trigger and looks up the timestamp by the old namespace, null value is returned.
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