---
title: "Successfully Merging the Work of 1000+ Developers"
description: "Shopify’s single monolith supports changes 40 times a day and roughly 400 commits to master daily, making safe trunk-based development difficult at the scale of 1,000+ developers. Its first Merge Queue limited deployment drift and batch size, but queued pull requests did not receive CI, soft conflicts could break master, and a browser extension enabled accidental direct merges. Merge Queue v2 replaces that workflow with GitHub comments and webhooks, programmatic branch protection, an emergency /shipit --emergency path, and a predictive branch where queued changes receive CI before merging. A reconciliation algorithm synchronizes that branch through GitHub’s GraphQL API, while failure-tolerance thresholds handle flaky tests and remove repeatedly failing pull requests. CI starts when requests enter the queue; batches of eight and three concurrently tested batches balance throughput, risk, and resource use, while the changes improved user experience, deployment safety, and deploy throughput."
---

# Successfully Merging the Work of 1000+ Developers

[Shopify](https://yomu.fyi/company/shopify) · 2023-10-18 · Nov 14, 2019

**Type:** Problem & solution

## Summary

Shopify’s single monolith supports changes 40 times a day and roughly 400 commits to master daily, making safe trunk-based development difficult at the scale of 1,000+ developers. Its first Merge Queue limited deployment drift and batch size, but queued pull requests did not receive CI, soft conflicts could break master, and a browser extension enabled accidental direct merges. Merge Queue v2 replaces that workflow with GitHub comments and webhooks, programmatic branch protection, an emergency /shipit --emergency path, and a predictive branch where queued changes receive CI before merging. A reconciliation algorithm synchronizes that branch through GitHub’s GraphQL API, while failure-tolerance thresholds handle flaky tests and remove repeatedly failing pull requests. CI starts when requests enter the queue; batches of eight and three concurrently tested batches balance throughput, risk, and resource use, while the changes improved user experience, deployment safety, and deploy throughput.

## Context

Shopify needed to safely merge and deploy hundreds of daily commits across a large team and single codebase. Merge Queue v1 did not run CI while pull requests waited, allowing soft conflicts and broken merges; incidents could also create queues of more than 50 pull requests, while the browser extension enabled accidental direct merges.

## Approach / What changed

Merge Queue v2 integrates the merge workflow with GitHub through comments, webhooks, GraphQL, and programmatic branch protection. It uses a predictive branch for pre-merge CI, reconciliation to maintain the desired GitHub state, failure-tolerance thresholds for flaky tests, an emergency bypass command, and bounded batches to improve deployment throughput.

## Takeaways

- Merge Queue v2 starts CI as soon as a pull request enters the queue and uses a predictive branch to test the prospective state of master before merging.
- With an assumed 25% test flakiness rate, a failure tolerance of 3 reduces the false-positive probability to 0.39%; the first failing pull request is removed after a fourth consecutive failure.
- Shopify chose batches of eight pull requests and runs CI on three batches at a time, balancing deployment throughput and risk while limiting CI resource use.

**Tags:** [CI/CD](https://yomu.fyi/topic/ci-cd), [Deployment](https://yomu.fyi/topic/deployment), [GraphQL](https://yomu.fyi/topic/graphql), [Monoliths](https://yomu.fyi/topic/monolith), [Testing](https://yomu.fyi/topic/testing)

- Source: [Shopify](https://shopify.engineering/successfully-merging-work-1000-developers)
- Source URL: https://shopify.engineering/successfully-merging-work-1000-developers
- Ingested by Yomu: 2026-08-31T01:13:32.459Z

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