Build the test database once for all workers

Have one parallel worker apply the schema while the others wait for it, so more workers stop repeating the same setup.

Prompt

Evaluate and apply this CI technique to my repository: Build the test database once for all workers.

Have one parallel worker apply the schema while the others wait for it, so more workers stop repeating the same setup.

Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/coordinate-test-setup.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.

View all playbooks

How Ramp used this technique

Read what Ramp changed and follow the original sources.

Build the test database once for all workers

Ramp's test setup recreated the database from scratch by applying every migration, and each pytest-xdist worker ran that setup in parallel. At higher worker counts the concurrent schema changes ran Postgres out of working memory and repeated the same work. Ramp restructured the setup so one worker applies the schema, which let it run more workers on a machine twice the size.

Coordinating the schema setup let Ramp double the machine size and halve CI test times, which had been creeping up towards 20 minutes. Source

Use it when: Tests run in parallel workers that each repeat the same database or fixture setup, and raising the worker count stops paying off.
Before applying it: The other workers wait for the one that builds the schema, so the setup itself still sets a floor on the job's time.

How Ramp used this technique

Build the test database once for all workers

Related techniques

Isolate state before running tests in parallel

Match test concurrency to the runner

Move unit tests to a parallel-by-default framework, gated on ten clean runs

Company Playbooks

Related guides

Shard tests across parallel jobs

Cut repeated test setup

Diagnose slow tests in CI

Optimize Playwright tests

Make Vitest run mode explicit

Parallelize independent jobs