Reduce the setup floor before increasing shard count

Each extra shard repeats checkout, dependencies and container setup.

Prompt

Evaluate and apply this CI technique to my repository: Reduce the setup floor before increasing shard count.

Each extra shard repeats checkout, dependencies and container setup.

Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/setup-cost-limits-sharding.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 Linear used this technique

Read what Linear changed and follow the original sources.

Reduce the setup floor before increasing shard count

Each extra shard repeats checkout, dependencies and container setup. Before its setup work, Linear’s test job used 4 shards and spent 8.3 minutes on setup; afterward it ran 8 shards with 7.5 minutes of setup.

Use it when: More shards would repeat substantial fixed setup work.
Before applying it: Remeasure per-shard setup before changing shard count.

How Linear used this technique

Reduce the setup floor before increasing shard count

Related techniques

Install and build only the workspace packages a job uses

Bake stable dependencies into runner images

Balance test work across shards

Company Playbooks

Related guides

Cancel superseded CI runs

Build and test only what changed

Cut repeated test setup

Shard tests across parallel jobs

Filter workflows by changed files

Cut CI queue time