[CI] BucketCountKSTestAggregatorTests testKsTest_LowerTailedValues failing

[davidkyle]

Build scan:
https://gradle-enterprise.elastic.co/s/hjhqluh6kgo3k/tests/:x-pack:plugin:ml:test/org.elasticsearch.xpack.ml.aggs.kstest.BucketCountKSTestAggregatorTests/testKsTest_LowerTailedValues

Reproduction line:
./gradlew ':x-pack:plugin:ml:test' --tests "org.elasticsearch.xpack.ml.aggs.kstest.BucketCountKSTestAggregatorTests.testKsTest_LowerTailedValues" -Dtests.seed=9F6F4A063AC4B3AF -Dtests.locale=de-DE -Dtests.timezone=America/Cambridge_Bay -Druntime.java=11

Applicable branches:
master

Reproduces locally?:
Yes

Failure history:
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.ml.aggs.kstest.BucketCountKSTestAggregatorTests&tests.test=testKsTest_LowerTailedValues

Failure excerpt:

java.lang.AssertionError: two_sided
Expected: a numeric value within <0.25> of <0.27838292008175725>
     but: <0.018584154974416345> differed by <0.009798765107340901> more than delta <0.25>

  at __randomizedtesting.SeedInfo.seed([9F6F4A063AC4B3AF:BEF4A9954F899BCE]:0)
  at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
  at org.junit.Assert.assertThat(Assert.java:956)
  at org.elasticsearch.xpack.ml.aggs.kstest.BucketCountKSTestAggregatorTests.testKsTest_LowerTailedValues(BucketCountKSTestAggregatorTests.java:124)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(NativeMethodAccessorImpl.java:-2)
  at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:566)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$8.evaluate(RandomizedRunner.java:946)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$9.evaluate(RandomizedRunner.java:982)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:996)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:49)
  at org.apache.lucene.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:45)
  at org.apache.lucene.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:48)
  at org.apache.lucene.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:64)
  at org.apache.lucene.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:375)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:824)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:475)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:955)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:840)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:891)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:902)
  at org.apache.lucene.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:45)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:41)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:47)
  at org.apache.lucene.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:64)
  at org.apache.lucene.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:54)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:375)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.lambda$forkTimeoutingTask$0(ThreadLeakControl.java:831)
  at java.lang.Thread.run(Thread.java:834)

[elasticmachine]

Pinging @elastic/ml-core (Team:ML)

[dai-dao]

Hello, i investigated this issue briefly and found that the error occurred at this line:

assertThat(alternative,
                lessValsUniformSampled.get(alternative),
                closeTo(lessValsUniformSampledSparsed.get(alternative), 0.25));

and that the actual delta is 0.2597987651073409. An interesting observation is that if I comment out these lines which are unrelated to the error:

Map<String, Double> lessValsUpperSampled = runKsTestAndValidate(LOWER_TAILED_VALUES, new SamplingMethod.UpperTail());
Map<String, Double> lessValsUpperSampledSparsed = runKsTestAndValidate(LOWER_TAILED_VALUES_SPARSE, new SamplingMethod.UpperTail());
Map<String, Double> lessValsLowerSampled = runKsTestAndValidate(LOWER_TAILED_VALUES, new SamplingMethod.LowerTail());
Map<String, Double> lessValsLowerSampledSparsed = runKsTestAndValidate(LOWER_TAILED_VALUES_SPARSE, new SamplingMethod.LowerTail());

then the test will pass, which means that they are related to the number generator somehow. Cheers :)

[benwtrent]

@dai-dao 100% :). The issue with the sparse distribution is that it requires the scale to all be reduced. But consequently, the distribution starts to look more uniform. I have a change in flight to address this. Running 1,000s of times locally to make sure :)