GitLab Merge Train - How It Differs from Merge

Merge Train Features

Automated Merging Process

• Sequential merging of multiple merge requests (MRs)
• Automatic rebasing before merging
• Ensures the target branch remains up to date
• Reduces merge conflicts by merging MRs in a defined order

CI/CD Pipeline Efficiency

• Runs pipelines in a queue before merging
• Ensures each MR passes tests before integration
• Avoids redundant CI runs for multiple MRs
• Enhances pipeline efficiency and stability

Improved Collaboration

• MRs are added to the train automatically
• Developers don�t need to manually rebase MRs
• Ensures a predictable merge sequence
• Reduces bottlenecks in collaborative projects

Conflict Prevention & Resolution

• Detects conflicts before merging
• Allows developers to resolve conflicts before final integration
• Maintains clean and stable main branches
• Reduces the risk of last-minute merge failures

Parallel Execution & Queuing

• Supports multiple merge trains per target branch
• Runs tests for different MRs in parallel when possible
• Manages queued MRs efficiently
• Improves overall team productivity

Standard Merge Features

Manual Merge Process

• Developers merge MRs manually
• Requires rebasing or resolving conflicts individually
• Higher risk of introducing conflicts into the main branch

CI/CD Pipeline Execution

• Runs pipelines after merging into the target branch
• Does not guarantee stability before merging
• Might introduce errors if not tested properly before merging

Flexibility & Control

• Developers decide when and how to merge
• No predefined order for merging MRs
• More control over the process but requires manual intervention

Conflict Handling

• Conflicts are resolved before or after merging
• May cause delays if multiple developers work on the same branch
• Increases chances of main branch instability

Key Differences Between Merge Train & Standard Merge

Feature	Merge Train	Standard Merge
Merging Approach	Automated, sequential merging	Manual merging
CI/CD Execution	Runs pipelines before merging	Runs pipelines after merging
Conflict Detection	Pre-merge conflict detection	Post-merge conflict resolution
Rebasing	Automatic rebasing before merging	Requires manual rebasing
Branch Stability	Ensures stable target branch	Might introduce instabilities
Merge Order	Predefined and managed automatically	Unstructured and manual
Developer Effort	Reduced manual intervention	Requires manual handling

For more details, refer to the GitLab documentation.