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https://issues.apache.org/jira/browse/KYLIN-4397?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Shao Feng Shi resolved KYLIN-4397.
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Resolution: Fixed
> Use newLinkedHashMap in AssignmentUtil.java
> -------------------------------------------
>
> Key: KYLIN-4397
> URL: https://issues.apache.org/jira/browse/KYLIN-4397
> Project: Kylin
> Issue Type: Bug
> Components: Real-time Streaming
> Reporter: cpugputpu
> Assignee: cpugputpu
> Priority: Minor
> Fix For: v3.1.0, v3.0.2
>
>
> The tests in
> _org.apache.kylin.stream.coordinator.assign.DefaultAssignerTest#reBalanceTest_
> can fail and the failure is presented as follow.
> _java.lang.AssertionError: expected:<2> but was:<1>_
> _at
> org.apache.kylin.stream.coordinator.assign.DefaultAssignerTest.reBalanceTest(DefaultAssignerTest.java:165)_
> when executing _assertEquals(2, rsAssignment.size());_
>
> The root cause of this failure is when executing _Map<Integer, Map<String,
> List<Partition>>> result = assigner.reBalancePlan(rsList, cubes,
> existingAssignments);_ it will iterate over a HashMap. The stack trace is
> here:
> java.util.HashMap$EntrySet.iterator(HashMap.java:1014)
>
> org.apache.kylin.stream.coordinator.assign.DefaultAssigner.reBalancePlan(DefaultAssigner.java:93)
>
> org.apache.kylin.stream.coordinator.assign.DefaultAssignerTest.reBalanceTest(DefaultAssignerTest.java:163)_
> The specification about HashMap says that "this class makes no guarantees as
> to the order of the map; 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/HashMap.htm|https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html][l|https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html]
> The fix is to use LinkedHashMap instead of HashMap when initializing a Map.
> In this way, the non-deterministic behaviour is eliminated and the test will
> not suffer from the failure again. The code will be more stable.
>
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