[KYLIN-4397] Use newLinkedHashMap in AssignmentUtil.java

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: v3.1.0, v3.0.2
• Component/s: Real-time Streaming
• Assignee: cpugputpu
• Reporter: cpugputpu
• Created: 02/Mar/20 13:59
• Updated: 31/Jul/20 12:10
• Resolved: 26/Mar/20 15:11

Description

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[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.

 

Issue Links

• links to: GitHub Pull Request #1133