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https://issues.apache.org/jira/browse/FLINK-23886?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17404373#comment-17404373
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Arvid Heise edited comment on FLINK-23886 at 8/25/21, 11:49 AM:
----------------------------------------------------------------

{quote}
Flink actually synchronizes invocations of onTimer() and processElement() [see 
timers 
description|https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/dev/datastream/operators/process_function/#timers]
 via [mail box thread 
modle|https://github.com/apache/flink/blob/master/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java#L1665-L1671]
 in StreamTask. As far as I can see, I cannot see concurrent problem here.

Mabe [~arvid] could share more insights here.
{quote}
This is only true since Flink 1.11. Before that a few things were done 
concurrently, so I could imagine that there are bugs lingering. [~pnowojski] 
probably knows more.

However, this probably also means that none of the currently supported version 
would exhibit the same issue. So even if we manage to find the bug and fix it, 
there won't be a bugfix release; you'd have to apply a patch on your own.


was (Author: arvid):
{quote}
Flink actually synchronizes invocations of onTimer() and processElement() [see 
timers 
description|https://ci.apache.org/projects/flink/flink-docs-release-1.13/docs/dev/datastream/operators/process_function/#timers]
 via [mail box thread 
modle|https://github.com/apache/flink/blob/master/flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/tasks/StreamTask.java#L1665-L1671]
 in StreamTask. As far as I can see, I cannot see concurrent problem here.

Mabe [~arvid] could share more insights here.
{quote}
This is only true since Flink 1.11. Before that a few things were done 
concurrently, so I could imagine that there are bugs lingering. [~pnowojski] 
probably knows more.

However, this probably also means that none of the currently supported version 
would exhibit the same issue. So even we manage to find the bug and fix it, 
there won't be a bugfix release; you'd have to apply a patch on your own.

> An exception is thrown out when recover job timers from checkpoint file
> -----------------------------------------------------------------------
>
>                 Key: FLINK-23886
>                 URL: https://issues.apache.org/jira/browse/FLINK-23886
>             Project: Flink
>          Issue Type: Bug
>          Components: Runtime / State Backends
>            Reporter: JING ZHANG
>            Priority: Major
>         Attachments: image-2021-08-25-16-38-04-023.png, 
> image-2021-08-25-16-38-12-308.png, image-2021-08-25-17-06-29-806.png, 
> image-2021-08-25-17-07-38-327.png
>
>
> A user report the bug in the [mailist. 
> |http://mail-archives.apache.org/mod_mbox/flink-user/202108.mbox/%3ccakmsf43j14nkjmgjuy4dh5qn2vbjtw4tfh4pmmuyvcvfhgf...@mail.gmail.com%3E]I
>  paste the content here.
> Setup Specifics:
>  Version: 1.6.2
>  RocksDB Map State
>  Timers stored in rocksdb
>   
>  When we have this job running for long periods of time like > 30 days, if 
> for some reason the job restarts, we encounter "Error while deserializing the 
> element". Is this a known issue fixed in later versions? I see some changes 
> to code for FLINK-10175, but we don't use any queryable state 
>   
>  Below is the stack trace
>   
>  org.apache.flink.util.FlinkRuntimeException: Error while deserializing the 
> element.
> at 
> org.apache.flink.contrib.streaming.state.RocksDBCachingPriorityQueueSet.deserializeElement(RocksDBCachingPriorityQueueSet.java:389)
> at 
> org.apache.flink.contrib.streaming.state.RocksDBCachingPriorityQueueSet.peek(RocksDBCachingPriorityQueueSet.java:146)
> at 
> org.apache.flink.contrib.streaming.state.RocksDBCachingPriorityQueueSet.peek(RocksDBCachingPriorityQueueSet.java:56)
> at 
> org.apache.flink.runtime.state.heap.KeyGroupPartitionedPriorityQueue$InternalPriorityQueueComparator.comparePriority(KeyGroupPartitionedPriorityQueue.java:274)
> at 
> org.apache.flink.runtime.state.heap.KeyGroupPartitionedPriorityQueue$InternalPriorityQueueComparator.comparePriority(KeyGroupPartitionedPriorityQueue.java:261)
> at 
> org.apache.flink.runtime.state.heap.HeapPriorityQueue.isElementPriorityLessThen(HeapPriorityQueue.java:164)
> at 
> org.apache.flink.runtime.state.heap.HeapPriorityQueue.siftUp(HeapPriorityQueue.java:121)
> at 
> org.apache.flink.runtime.state.heap.HeapPriorityQueue.addInternal(HeapPriorityQueue.java:85)
> at 
> org.apache.flink.runtime.state.heap.AbstractHeapPriorityQueue.add(AbstractHeapPriorityQueue.java:73)
> at 
> org.apache.flink.runtime.state.heap.KeyGroupPartitionedPriorityQueue.<init>(KeyGroupPartitionedPriorityQueue.java:89)
> at 
> org.apache.flink.contrib.streaming.state.RocksDBKeyedStateBackend$RocksDBPriorityQueueSetFactory.create(RocksDBKeyedStateBackend.java:2792)
> at 
> org.apache.flink.contrib.streaming.state.RocksDBKeyedStateBackend.create(RocksDBKeyedStateBackend.java:450)
> at 
> org.apache.flink.streaming.api.operators.InternalTimeServiceManager.createTimerPriorityQueue(InternalTimeServiceManager.java:121)
> at 
> org.apache.flink.streaming.api.operators.InternalTimeServiceManager.registerOrGetTimerService(InternalTimeServiceManager.java:106)
> at 
> org.apache.flink.streaming.api.operators.InternalTimeServiceManager.getInternalTimerService(InternalTimeServiceManager.java:87)
> at 
> org.apache.flink.streaming.api.operators.AbstractStreamOperator.getInternalTimerService(AbstractStreamOperator.java:764)
> at 
> org.apache.flink.streaming.api.operators.KeyedProcessOperator.open(KeyedProcessOperator.java:61)
> at 
> org.apache.flink.streaming.runtime.tasks.StreamTask.openAllOperators(StreamTask.java:424)
> at 
> org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:290)
> at org.apache.flink.runtime.taskmanager.Task.run(Task.java:711)
> at java.lang.Thread.run(Thread.java:748)
> Caused by: java.io.EOFException
> at java.io.DataInputStream.readUnsignedByte(DataInputStream.java:290)
> at org.apache.flink.types.StringValue.readString(StringValue.java:769)
> at 
> org.apache.flink.api.common.typeutils.base.StringSerializer.deserialize(StringSerializer.java:69)
> at 
> org.apache.flink.api.common.typeutils.base.StringSerializer.deserialize(StringSerializer.java:28)
> at 
> org.apache.flink.api.java.typeutils.runtime.RowSerializer.deserialize(RowSerializer.java:179)
> at 
> org.apache.flink.api.java.typeutils.runtime.RowSerializer.deserialize(RowSerializer.java:46)
> at 
> org.apache.flink.streaming.api.operators.TimerSerializer.deserialize(TimerSerializer.java:168)
> at 
> org.apache.flink.streaming.api.operators.TimerSerializer.deserialize(TimerSerializer.java:45)
> at 
> org.apache.flink.contrib.streaming.state.RocksDBCachingPriorityQueueSet.deserializeElement(RocksDBCachingPriorityQueueSet.java:387)
> ... 20 more



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