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On this page
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  1. Merge Queue
  2. Concepts and Optimizations

Anti-Flake Protection

Using optimistic merging and pending-failure-depth to protect your Merge Queue from flaky failures

Last updated 1 month ago

Some CI jobs fail for reasons unrelated to a PR's code change, such as due to or a CI runner disconnecting. These failures are usually cleared when the CI job is rerun. If a second PR that depends on the first does pass, it is very likely that the first PR was good and simply experienced a transient failure. Trunk Merge Queue can use the combination of and to merge pull requests that would otherwise be rejected from the queue.

If you have a lot of flaky tests in your projects, you should track and fix them with . Anti-flake protection helps reduce the impact of flaky tests but doesn't help you detect, track, and eliminate them.

In the video below, you can see an example of this anti-flake protection:

what's happening?
queue

A, B, C begin predictive testing

main <- A <- B+a <- C+ba

B fails testing

main <- A <- B+a <- C+ba

predictive failure depth keeps B from being evicted while C tests

main <- A <- B+a (hold) <- C+ba

C passes

main <- A <- B+a <- C+ba

optimistic merging allows A, B, C to merge

merge A B C

Enabling anti-flake protection

What are the tradeoffs?

When optimistic merging is used, there is a small tradeoff to be made. You can get into a situation where an actually broken test in, say, change 'B' is corrected by a change in 'C'. In this case, if you later reverted to 'C', your build would be broken.

Optimistic Merging only works when the is set to a value greater than zero. When zero or disabled, Merge will not hold any failed tests in the queue.

To protect your merge queue from flakes, enable anti-flake protection by enabling and setting to an integer greater than 0 in the settings:

Optimistic Merge
Pending Failure Depth
Merge UI
Pending Failure Depth
flaky tests
Optimistic Merging
Trunk Flaky Tests
Pending Failure Depth
Anti-flake protection with optimistic merging + pending failure depth
Setting to enable anti-flake protection