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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7949) AsyncWaitOperator is not restarting when queue is full
Date Thu, 28 Dec 2017 16:15:04 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7949?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16305562#comment-16305562
] 

ASF GitHub Bot commented on FLINK-7949:
---------------------------------------

Github user bartektartanus commented on the issue:

    https://github.com/apache/flink/pull/4924
  
    Hi @tillrohrmann 
    I've finally managed to write a simple test that fails without my change in AsyncWaitOperator
class. Test steps:
    1. add enough records to fill up the AsyncWaitOperator queue
    2. add record which processing takes more time than timeout which causes restart
    3. data stream is restarted and in `open()` method it tries to add N+1 recovered stream
elements to queue of size N
    4. test waits forever and fails due to timeout. 
    
    Works exactly as I've mentioned before. But if the emitter is started earlier, eventually
test passes after two restarts (`timeoutCounter` field in `TimeoutableFunction`). Tried to
make this test as short and quick as possible. I don't know if this is the right file for
this, please fix this if so. I also hope this change will be in next flink version :) 
    Happy New Year!


> AsyncWaitOperator is not restarting when queue is full
> ------------------------------------------------------
>
>                 Key: FLINK-7949
>                 URL: https://issues.apache.org/jira/browse/FLINK-7949
>             Project: Flink
>          Issue Type: Bug
>          Components: Streaming
>    Affects Versions: 1.3.2
>            Reporter: Bartłomiej Tartanus
>            Priority: Critical
>   Original Estimate: 0.25h
>  Remaining Estimate: 0.25h
>
> Issue was describe here:
> http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Checkpoint-was-declined-tasks-not-ready-td16066.html
> Issue - AsyncWaitOperator can't restart properly after failure (thread is waiting forever)
> Scenario to reproduce this issue:
> 1. The queue is full (let's assume that its capacity is N elements) 
> 2. There is some pending element waiting, so the 
> pendingStreamElementQueueEntry field in AsyncWaitOperator is not null and 
> while-loop in addAsyncBufferEntry method is trying to add this element to 
> the queue (but element is not added because queue is full) 
> 3. Now the snapshot is taken - the whole queue of N elements is being 
> written into the ListState in snapshotState method and also (what is more 
> important) this pendingStreamElementQueueEntry is written to this list too. 
> 4. The process is being restarted, so it tries to recover all the elements 
> and put them again into the queue, but the list of recovered elements hold 
> N+1 element and our queue capacity is only N. Process is not started yet, so 
> it can not process any element and this one element is waiting endlessly. 
> But it's never added and the process will never process anything. Deadlock. 
> 5. Trigger is fired and indeed discarded because the process is not running 
> yet. 



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