A code freeze is a period during which changes to the production codebase are restricted, typically to ensure stability during critical times like holidays or major releases. However, development doesn't stop during a freeze. Developers continue to work on features and fixes, leading to a backlog of pull requests (PRs). A merge queue helps manage this backlog by organizing and automating the merging process once the freeze is lifted, ensuring a smooth transition back to normal operations.
Benefits of using a merge queue during a code freeze
1. Controlled merging post-freeze A merge queue sequences PRs, allowing them to be merged one at a time or in batches after the freeze. This controlled approach prevents integration issues that can arise from merging multiple PRs simultaneously.
2. Continuous validation Even during a freeze, PRs can be added to the queue and undergo automated testing. This ensures that once the freeze ends, only validated and conflict-free PRs are merged, maintaining code quality.
3. Handling urgent fixes In cases where critical fixes are needed during a freeze, merge queues allow for prioritization. Some tools support priority management, enabling urgent PRs to be merged ahead of others once approved.
Implementing a merge queue during a code freeze
1. Setting up the merge queue Tools like Graphite offer merge queue functionalities. For instance, Graphite integrates with GitHub and allows for stacked PRs, where changes are built upon each other in a sequence. This is particularly useful during a freeze as it organizes dependent changes effectively.
2. Freezing the queue During a code freeze, it's essential to prevent automatic merging. Mergify provides a "Queue Freeze" feature that halts the merging process without stopping the validation of PRs. This ensures that PRs are ready to merge once the freeze is lifted.
3. Managing the queue post-freeze After the freeze, the merge queue can resume operations. Tools like the Graphite Merge Queue support batching, where multiple PRs are merged together after passing combined tests, improving efficiency.
Best practices
Communicate clearly: Inform the development team about the freeze schedule and the process for handling PRs during this period.
Prioritize critical fixes: Establish criteria for what constitutes an urgent fix and how it will be handled during the freeze.
Maintain CI/CD pipelines: Ensure that automated tests continue to run on queued PRs to catch issues early.
Review and update: After the freeze, review the queued PRs for any changes in priority or relevance before merging.
Conclusion
Using a merge queue during a code freeze allows development to continue without compromising the stability of the production codebase. By organizing, validating, and prioritizing PRs, teams can ensure a smooth transition back to normal operations post-freeze. Tools like Graphite and Mergify provide robust solutions for managing merge queues effectively.