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Posted to issues@kylin.apache.org by "ASF GitHub Bot (Jira)" <ji...@apache.org> on 2020/03/02 14:05:00 UTC
[jira] [Commented] (KYLIN-4397) Use newLinkedHashMap in
AssignmentUtil.java
[ https://issues.apache.org/jira/browse/KYLIN-4397?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17049234#comment-17049234 ]
ASF GitHub Bot commented on KYLIN-4397:
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cpugputpu commented on pull request #1133: KYLIN-4397 Use newLinkedHashMap for deterministic order in AssignmentUtil.java
URL: https://github.com/apache/kylin/pull/1133
This PR aims to solve the issue here: https://issues.apache.org/jira/browse/KYLIN-4397
The fix is to use `newLinkedHashMap` instead of `newHashMap` 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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> Use newLinkedHashMap in AssignmentUtil.java
> -------------------------------------------
>
> Key: KYLIN-4397
> URL: https://issues.apache.org/jira/browse/KYLIN-4397
> Project: Kylin
> Issue Type: Bug
> Reporter: cpugputpu
> Priority: Minor
>
> 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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