[jira] [Commented] (FLINK-16349) Use LinkedHashSet in TimeWindow.java

["Chesnay Schepler (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-16349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17048366#comment-17048366 ] 

Chesnay Schepler commented on FLINK-16349:
------------------------------------------

What makes you think that the element is the problem? The test assertions clearly don't care about the order:
{{code}
iterable over <TimeWindow{start=0, end=3}>, <TimeWindow{start=5, end=8}> in any order
{{code}}

The actual problem is that the TimeWindow start is one in the actual value, but 0 in all expected cases.

> Use LinkedHashSet in TimeWindow.java
> ------------------------------------
>
>                 Key: FLINK-16349
>                 URL: https://issues.apache.org/jira/browse/FLINK-16349
>             Project: Flink
>          Issue Type: Bug
>            Reporter: cpugputpu
>            Priority: Minor
>              Labels: pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> The test in _apache.flink,org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSetTest#testMergeLargeWindowCoveringMultipleWindows_ can fail due to a different iteration order of HashSet.
> The failure is presented as follows.
> java.lang.AssertionError: java.lang.AssertionError: 
> *Expected*: (iterable over <TimeWindow\{start=0, end=3}>, <TimeWindow\{start=5, end=8}> in any order or iterable over <TimeWindow\{start=0, end=3}>, <TimeWindow\{start=10, end=13}> in any order or iterable over <TimeWindow\{start=5, end=8}>, <TimeWindow\{start=10, end=13}> in any order)
> *but was*: <TimeWindow\{start=1, end=3}, TimeWindow\{start=10, end=13}> at org.apache.flink.streaming.runtime.operators.windowing.MergingWindowSetTest.testMergeLargeWindowCoveringMultipleWindows(MergingWindowSetTest.java:358)
>  
> The root cause of it lies in TimeWindow.java, where _currentMerge.f1 = new LinkedHashSet<>();_ is executed. When calling _W mergedStateWindow = this.mapping.get(mergedWindows.iterator().next());_ (flink-streaming-java/src/main/java/org/apache/flink/streaming/runtime/operators/windowing/MergingWindowSet.java , line 192), the _iterator()_ of HashSet will make no guarantee about the order.
> The specification about HashSet says that "it makes no guarantees as to the iteration order of the set; in particular, it does not guarantee that the order will remain constant over time". The documentation is here for your reference: [https://docs.oracle.com/javase/8/docs/api/java/util/HashSet.html]
>  
> The fix is to use LinkedHashSet instead of HashSet so that the non-deterministic behaviour is eliminated. The code will be more stable.



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