[Webkit-unassigned] [Bug 196096] Many failures caused by async overflow scrolling weren't caught by EWS

bugzilla-daemon at webkit.org bugzilla-daemon at webkit.org
Thu Mar 21 20:08:39 PDT 2019


https://bugs.webkit.org/show_bug.cgi?id=196096

--- Comment #3 from Alexey Proskuryakov <ap at webkit.org> ---
So... why did it not cause these failures on EWS?

The only difference between EWS and post-commit bots is that EWS enables retries, thus hiding some flakiness. This is not good, but EWS can't function with the current level of flakiness, and it's better to hide some failures sometimes than to lose EWS entirely.

If these 100+ failures were hidden by retry, that's bad news. I can think of several explanations:
- A state leak between tests. If these tests only fail when run after some test that passes but leaks state (such as preferences), then they will pass on retry.
- Severe timing dependency. Retries are serial, so tests that can't run on a busy machine will pass on retry.
- Similar to #1, but persistent conditions related to iOS simulator state, not WebKit state.

In any of these cases, it sounds like there will be more work fixing things in WebKit.

Alternatively, if there is some other mysterious reason, then it is, well, mysterious.

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