[FLINK-29789] Fix flaky tests in CheckpointCoordinatorTest

• Type: Bug
• Status: Open
• Priority: Not a Priority
• Resolution: Unresolved
• Labels: auto-deprioritized-minor pull-request-available
• Assignee: Unassigned
• Reporter: Sopan Phaltankar
• Created: 28/Oct/22 04:44
• Updated: 18/Aug/23 22:35

Description

The test org.apache.flink.runtime.checkpoint.CheckpointCoordinatorTest.testTriggerAndDeclineCheckpointComplex is flaky and has the following failure:

Failures:
[ERROR] Failures:
[ERROR]   CheckpointCoordinatorTest.testTriggerAndDeclineCheckpointComplex:1054 expected:<2> but was:<1>

I used the tool NonDex to find this flaky test.
Command: mvn -pl flink-runtime edu.illinois:nondex-maven-plugun:1.1.2:nondex -Dtest=org.apache.flink.runtime.checkpoint.CheckpointCoordinatorTest#testTriggerAndDeclineCheckpointComplex

I analyzed the assertion failure and found that checkpoint1Id and checkpoint2Id are getting assigned by iterating over a HashMap.
As we know, iterator() returns elements in a random order (JavaDoc) and this might cause test failures for some orders.

Therefore, to remove this non-determinism, we would change HashMap to LinkedHashMap.
On further analysis, it was found that the Map is getting initialized on line 1894 of org.apache.flink.runtime.checkpoint.CheckpointCoordinator class.

After changing from HashMap to LinkedHashMap, the above test is passing without any non-determinism.

Issue Links

• links to: GitHub Pull Request #21183