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From "cpugputpu (Jira)" <j...@apache.org>
Subject [jira] [Created] (KYLIN-4397) Use newLinkedHashMap in stream-coordinator/src/main/java/org/apache/kylin/stream/coordinator/assign/AssignmentUtil.java
Date Mon, 02 Mar 2020 14:00:00 GMT
cpugputpu created KYLIN-4397:
--------------------------------

             Summary: Use newLinkedHashMap in stream-coordinator/src/main/java/org/apache/kylin/stream/coordinator/assign/AssignmentUtil.java
                 Key: KYLIN-4397
                 URL: https://issues.apache.org/jira/browse/KYLIN-4397
             Project: Kylin
          Issue Type: Bug
            Reporter: cpugputpu


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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