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https://issues.apache.org/jira/browse/FLINK-37670?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17945039#comment-17945039
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Piotr Nowojski commented on FLINK-37670:
----------------------------------------
merged commit ad51793 into apache:release-2.0
merged commit 5c24ae6 into apache:release-1.20
> Watermark alignment can deadlock job if there are no more splits to be
> assigned
> -------------------------------------------------------------------------------
>
> Key: FLINK-37670
> URL: https://issues.apache.org/jira/browse/FLINK-37670
> Project: Flink
> Issue Type: Bug
> Components: API / DataStream, Runtime / Task
> Affects Versions: 2.0.0, 1.19.2, 1.20.1
> Reporter: Piotr Nowojski
> Assignee: Piotr Nowojski
> Priority: Major
> Labels: pull-request-available
>
> {{SourceCoordinator#announceCombinedWatermark}} stops announcing combined
> watermark if {{context.hasNoMoreSplits(subtaskId)}} returns true.
> {noformat}
> for (Integer subtaskId : subTaskIds) {
> // when subtask have been finished, do not send event.
> if (!context.hasNoMoreSplits(subtaskId)) {
> // Subtask maybe during deploying or restarting, so we only
> send
> // WatermarkAlignmentEvent to ready task to avoid period task
> fail
> // (Java-ThreadPoolExecutor will not schedule the period task
> if it throws an
> // exception).
> context.sendEventToSourceOperatorIfTaskReady(
> subtaskId, new
> WatermarkAlignmentEvent(maxAllowedWatermark));
> }
> }
> {noformat}
> Which means new max allowed watermark will not be announced anymore,
> preventing sources from making progress. The intention was to prevent
> failures caused by tasks not running:
> {noformat}
> Caused by:
> org.apache.flink.runtime.operators.coordination.TaskNotRunningException: Task
> is not running, but in state FINISHED
> at
> org.apache.flink.runtime.taskmanager.Task.deliverOperatorEvent(Task.java:1613)
> ~[flink-runtime-1.19-SNAPSHOT.jar:1.19-SNAPSHOT]
> at
> org.apache.flink.runtime.taskexecutor.TaskExecutor.sendOperatorEventToTask(TaskExecutor.java:1478)
> ~[flink-runtime-1.19-SNAPSHOT.jar:1.19-SNAPSHOT]
> at jdk.internal.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
> ~[?:?]
> at
> jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
> ~[?:?]
> at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]
> at
> org.apache.flink.runtime.rpc.pekko.PekkoRpcActor.lambda$handleRpcInvocation$1(PekkoRpcActor.java:318)
> ~[flink-rpc-akka8c031913-bb13-4662-a216-58134efdb2d9.jar:1.19-SNAPSHOT]
> at
> org.apache.flink.runtime.concurrent.ClassLoadingUtils.runWithContextClassLoader(ClassLoadingUtils.java:83)
> ~[flink-rpc-core-1.19-SNAPSHOT.jar:1.19-SNAPSHOT]
> at
> org.apache.flink.runtime.rpc.pekko.PekkoRpcActor.handleRpcInvocation(PekkoRpcActor.java:316)
> ~[flink-rpc-akka8c031913-bb13-4662-a216-58134efdb2d9.jar:1.19-SNAPSHOT]
> at
> org.apache.flink.runtime.rpc.pekko.PekkoRpcActor.handleRpcMessage(PekkoRpcActor.java:229)
> ~[flink-rpc-akka8c031913-bb13-4662-a216-58134efdb2d9.jar:1.19-SNAPSHOT]
> {noformat}
> but:
> # This is an incorrect check. This, contrary to the comment, doesn't check if
> all subtasks have finished, but only that source coordinator has no more
> splits to assign.
> # Even if it was checking if all subtasks finished, that wouldn't work
> because:
> * one subtask can be finished, while others are still running
> * there can be race conditions between sending an operator event to a
> running operator and that operator switching to finished
> I think, at least for some non critical events, we need to just ignore
> {{TaskNotRunningException}}.
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