[Webkit-unassigned] [Bug 195961] New: [ Mojave Debug ] REGRESSION (r242975) Layout Test imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex7-event_order.html is a flaky failure

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=195961

            Bug ID: 195961
           Summary: [ Mojave Debug ] REGRESSION (r242975) Layout Test
                    imported/w3c/IndexedDB-private-browsing/idbobjectstore
                    _createIndex7-event_order.html is a flaky failure
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Tools / Tests
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sroberts at apple.com
                CC: lforschler at apple.com

The following layout test is flaky on Mojave Debug WK2

imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex7-event_order.html
imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex6-event_order.html

Probable cause:

Test recently showed up on the dashboard ~242943. Recently started to be more flaky. 

Through testing found that as of r242975 the failure rate jumped to about 25/600 failures. Exited early with 25 failures around 600 iterations. 
Testing prior to 242975 show that the test was a highly flaky failure, only 1 or 2 failures in 1500 iterations. I tested with various builds from 242974 to 242400 for these results.
Dashboard also shows flaky failures with WK1, iOS Simulator Debug, and Mac WK2. Those have similar highly flaky results, but did not get worse with 242943 like it did with Mojave Debug WK2.

Reproduced with: 

run-webkit-tests imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex6-event_order.html --iterations 1500 -f --debug --exit-after-n-failures=25 --no-retry

Flakiness Dashboard:

https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=imported%2Fw3c%2FIndexedDB-private-browsing%2Fidbobjectstore_createIndex7-event_order.html

Index 7 Diff: 

--- /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex7-event_order-expected.txt
+++ /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex7-event_order-actual.txt
@@ -1,3 +1,3 @@

-PASS IDBObjectStore.createIndex() - Event ordering for ConstraintError on request 
+FAIL IDBObjectStore.createIndex() - Event ordering for ConstraintError on request assert_array_equals: events lengths differ, expected 10 got 8

Index 6 Diff:

--- /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex6-event_order-expected.txt
+++ /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/imported/w3c/IndexedDB-private-browsing/idbobjectstore_createIndex6-event_order-actual.txt
@@ -1,3 +1,3 @@

-PASS IDBObjectStore.createIndex() - event order when unique constraint is triggered 
+FAIL IDBObjectStore.createIndex() - event order when unique constraint is triggered assert_array_equals: events lengths differ, expected 8 got 6

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