What Is a Merge Queue?
A merge queue is a system that lines up approved pull requests and merges them one at a time, re-running CI on each against the up-to-date target branch before it lands. This prevents the situation where two PRs each pass independently but break when combined. It keeps a busy main branch continuously green without manual rebasing.
Why it matters
On high-traffic repos, a PR that was green an hour ago may conflict logically with what merged since. A merge queue tests the actual post-merge state for each change, catching these semantic conflicts. The trade-off is more CI runs, which fast, autoscaled runners help absorb.
Related concepts
- Tests each PR against the current target branch
- Prevents semantic conflicts between independently green PRs
- Increases CI load, favoring autoscaled runners
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