--- title: "Merge without re-testing against the latest main, except migrations" description: "Drop the up-to-date-with-main merge rule, test the main branch before every deploy, and make database migrations conflict in Git so only they must update." url: https://starsling.dev/ci-playbooks/techniques/merge-without-retest canonicalUrl: https://starsling.dev/ci-playbooks/techniques/merge-without-retest --- # Merge without re-testing against the latest main, except migrations Drop the up-to-date-with-main merge rule, test the main branch before every deploy, and make database migrations conflict in Git so only they must update. ## How to choose an approach This technique currently has one documented company example. Validate its prerequisites, tradeoffs and original CI environment against your repository before adapting it. - **[Ramp](https://starsling.dev/ci-playbooks/ramp#merge-without-retest)**: Use it when Most pull requests touch independent code, a branch rule makes each one re-run the full suite after every merge, and the main branch can run the suite before each deploy. Check before adopting: Two pull requests that pass separately can still fail together; the test run on the main branch before deployment is what catches that, so it stays required. ## Apply this technique ````text Evaluate and apply this CI technique to my repository: Merge without re-testing against the latest main, except migrations. Drop the up-to-date-with-main merge rule, test the main branch before every deploy, and make database migrations conflict in Git so only they must update. Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/merge-without-retest.md Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence. Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured. Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo. Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES. Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch. Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge. ```` ## How Ramp used this technique Read what Ramp changed and follow the original sources. ### Ramp: Merge without re-testing against the latest main, except migrations Every merge made the other open pull requests out of date with the main branch, so each one re-ran the 12-minute suite before it could merge, and with five in the queue the average pull request waited over an hour. Ramp removed the rule that pull requests must be up to date with the main branch and required the tests to pass on the main branch before any deployment. Two branches that each add a database migration from the same revision pass on their own but leave two migration heads once both merge, so Ramp committed migrations/migration-hash.txt, a hash of every migration filename: any two pull requests that add migrations conflict in Git, and the second must update. Evidence: Company-reported result or observation 2022: The average time to merge decreased from 1+ hour to 12 minutes, the time the test suite takes to run. ([Source](https://builders.ramp.com/post/merge-queues)) Use it when: Most pull requests touch independent code, a branch rule makes each one re-run the full suite after every merge, and the main branch can run the suite before each deploy. Before applying it: Two pull requests that pass separately can still fail together; the test run on the main branch before deployment is what catches that, so it stays required. [Read more in the Ramp playbook](https://starsling.dev/ci-playbooks/ramp#merge-without-retest) [Primary source](https://builders.ramp.com/post/merge-queues) ## CI optimization is continuous work. Apply this technique yourself, or use StarSling Runners for faster GitHub Actions and optional agent-driven optimization PRs, which teams on eligible paid plans can turn on. [Get self-improving CI](https://starsling.dev/products/runners) ## Company Playbooks ### [Anthropic](https://starsling.dev/ci-playbooks/anthropic) Run only affected tests ### [DoorDash](https://starsling.dev/ci-playbooks/doordash) Run build and test in parallel, sharded across CI agents ### [Linear](https://starsling.dev/ci-playbooks/linear) Benchmark the same job on faster hardware ### [Mastra](https://starsling.dev/ci-playbooks/mastra) StarSling runners for the slowest test workflow ### [OpenAI](https://starsling.dev/ci-playbooks/openai) Rank CI fixes by the minutes they save ### [Ramp](https://starsling.dev/ci-playbooks/ramp) Move a CPU-bound test suite to a faster CPU ### [Shopify](https://starsling.dev/ci-playbooks/shopify) Let an agent iterate against one CI metric ### [Spotify](https://starsling.dev/ci-playbooks/spotify) Build arm64 on native arm64 runners ### [Stripe](https://starsling.dev/ci-playbooks/stripe) Run only the tests a change can reach ### [Uber](https://starsling.dev/ci-playbooks/uber) Build the merge-queue speculations most likely to be needed