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https://issues.apache.org/jira/browse/FLINK-16349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17321409#comment-17321409
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Flink Jira Bot commented on FLINK-16349:
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This issue and all of its Sub-Tasks have not been updated for 180 days. So, it
has been labeled "stale-minor". If you are still affected by this bug or are
still interested in this issue, please give an update and remove the label. In
7 days the issue will be closed automatically.
> Use LinkedHashSet in TimeWindow.java
> ------------------------------------
>
> Key: FLINK-16349
> URL: https://issues.apache.org/jira/browse/FLINK-16349
> Project: Flink
> Issue Type: Bug
> Components: API / DataStream
> Reporter: cpugputpu
> Priority: Minor
> Labels: pull-request-available, stale-minor
> Time Spent: 20m
> 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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