Git Merge vs Rebase Demystified: A Deep Dive into Version Control Mastery

Version control is critical in managing code for development teams. In Git, MERGE and REBASE are two important strategies for integrating changes from one branch into another. Both are powerful tools, but knowing when and how to use them is key for a cleaner commit history and conflict-free collaboration.

What is Git MERGE?

A merge combines the histories of two branches into a single branch. It creates a new commit called a “merge commit” to signify where the branches were merged.

Example Scenario: MERGING Two Branches

# Assume you're on the 'feature' branch
git checkout feature

# Merge 'main' into 'feature'
git merge main

Here’s a visualization before and after the merge:

Diagram: Before and After a Merge

Before Merge:

A---B---C  (main)
     \
      D---E  (feature)

After Merge:

A---B---C-------F  (main)
     \       /
      D---E  (feature)

In this case, the F commit is the merge commit that combines both branches.

Pros of Using Git MERGE

• Preserves history: It keeps the original history intact, making it easy to trace.
• Easier conflict resolution: All changes are merged into a single commit.

Cons of Using Git MERGE

• Extra merge commits: The commit history can become cluttered with merge commits.
• Less linear history: The history can become harder to follow when working with multiple feature branches.

What is Git REBASE?

A rebase moves the entire feature branch to begin from the tip of the main branch. It effectively “replays” your feature branch’s changes on top of the main branch.

Example Scenario: REBASING a Feature Branch

# Assume you're on the 'feature' branch
git checkout feature

# Rebase the 'feature' branch on top of 'main'
git rebase main

This moves the feature branch to start from the latest commit in main.

Diagram: Before and After a Rebase

Before Rebase:

A---B---C  (main)
     \
      D---E  (feature)

After Rebase:

A---B---C---D'---E'  (main, feature)

Note that D' and E' are new commits that represent the rebased changes from the feature branch.

Pros of Using Git REBASE

• Cleaner history: The history looks linear, with no extra merge commits.
• Easier to follow: Linear history makes it easier to debug and understand the commit flow.

Cons of Using Git REBASE

• Rewriting history: Rebasing rewrites commit history, which can be confusing.
• Potential for conflicts: Rebasing can cause more complex conflicts, especially if both branches have overlapping changes.

When to Use MERGE vs REBASE?

How to Resolve Conflicts in Git MERGE

If conflicts occur during a merge, Git will pause and ask you to resolve them. Here’s how you can resolve disputes:

git merge main
# If there's a conflict, Git will notify you. Now manually resolve the conflicts in the files.
# After resolving conflicts, continue with:
git add <resolved-files>
git commit

How to Resolve Conflicts in Git REBASE

Rebasing can also lead to conflicts. Here’s how to resolve them during a rebase:

git rebase main
# Git will pause and notify you of conflicts.
# After resolving conflicts, continue the rebase with:
git rebase --continue

Visualizing Git History Using git log

To better visualize your Git history, you can use the following command:

git log --oneline --graph --all

This command shows a graph of your commit history, making it easy to see the difference between merged and rebased histories.

Visualization of Merge History

*   F Merge branch 'main' into 'feature'
|\
| * C Commit on main
| * B Commit on main
* | E Commit on feature
* | D Commit on feature
|/
* A Initial commit

Visualization of Rebase History

* E' Commit on feature
* D' Commit on feature
* C Commit on main
* B Commit on main
* A Initial commit

Conclusion

In summary, both MERGE and REBASE are powerful tools in Git for integrating changes between branches. Each has its pros and cons, and the choice between them depends on the project structure and your team’s workflow.

• Use MERGE when you want to preserve the complete history of how branches were combined.
• Use REBASE when you want a cleaner, more linear history.

By mastering both, you’ll have greater control over your codebase and will be able to manage complex workflows with ease.

Bonus Tip: Always communicate with your team before performing a rebase, especially if others are working on the same branch, as rebasing rewrites history!

References

• Git Documentation: https://git-scm.com/doc