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https://issues.apache.org/jira/browse/FLINK-7606?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16197094#comment-16197094
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Kostas Kloudas commented on FLINK-7606:
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I do not think that this would solve the problem. 
In event time, an element that has a timestamp X does not mean that also the 
event time has advanced passed that time. 
The watermark is the one that signals that time has advanced. So if the 
watermark does not advance, we cannot be sure that we can close a window. 

Only if you know your data, _e.g._ that timestamps are in order, then you can 
assume that. 
But in this case you could probably write your own timestamp extractor, that 
after a timeout, it sends a watermark with the "correct" timestamp.

> CEP operator leaks state
> ------------------------
>
>                 Key: FLINK-7606
>                 URL: https://issues.apache.org/jira/browse/FLINK-7606
>             Project: Flink
>          Issue Type: Bug
>          Components: CEP
>    Affects Versions: 1.3.1
>            Reporter: Matteo Ferrario
>         Attachments: Schermata 2017-09-27 alle 00.35.53.png, heap-dump1.png, 
> heap-dump2.png, heap-dump3.png
>
>
> The NestedMapsStateTable grows up continuously without free the heap memory.
> We created a simple job that processes a stream of messages and uses CEP to 
> generate an outcome message when a specific pattern is identified.
> The messages coming from the stream are grouped by a key defined in a 
> specific field of the message.
> We've also added the "within" clause (set as 5 minutes), indicating that two 
> incoming messages match the pattern only if they come in a certain time 
> window.
> What we've seen is that for every key present in the message, an NFA object 
> is instantiated in the NestedMapsStateTable and it is never deallocated.
> Also the "within" clause didn't help: we've seen that if we send messages 
> that don't match the pattern, the memory grows up (I suppose that the state 
> of NFA is updated) but it is not cleaned also after the 5 minutes of time 
> window defined in "within" clause.
> If you need, I can provide more details about the job we've implemented and 
> also the screenshots about the memory leak.



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