Difference Between Merge and Rebase

Summary:
When to use git merge vs git rebase.

Version control is at the heart of software development, and Git is the undisputed leader in this space. Among its many features, the ability to integrate changes from one branch into another is crucial for development workflows. Two primary commands used for this purpose are git merge and git rebase. While both seem to accomplish the same goal — integrating changes — they do so in fundamentally different ways. Understanding the distinction is critical for maintaining a clean, understandable project history.

What is Git Merge?

git merge creates a new merge commit that ties together the histories of two branches. This process preserves the exact historical lineage of both branches, creating a non-linear, "true" record of events.

How it Works:

Suppose you have two branches: main and feature (with unique commits on each).

# On feature branch, update from main
git checkout feature
git merge main

Diagram:

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

After merging main into feature, the history might look like:

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

(G is the new merge commit.)

Pros:

  • Preserves full context and chronological order: History shows all commits and both branch paths.
  • Avoids rewriting commits: Safer when collaborating, especially with published branches.
  • Clear 'merge points': You can see exactly when branches rejoined.

Cons:

  • Can clutter history: Especially with complex branching, the commit tree can become tangled.
  • Merge commits can add noise.

What is Git Rebase?

git rebase moves (or "replays") the entire branch's commits onto another base tip, creating a linear history. Rebasing rewrites commit hashes and places your changes as if they happened after the tip of the target branch.

How it Works:

Take the same scenario:

git checkout feature
git rebase main

Diagram (Before Rebase):

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

After Rebase:

A---B---C---D'---E'---F' (feature)

Notice how commits D, E, and F now follow C directly, becoming D', E', and F' (new commit IDs, as rewritten).

Pros:

  • Creates a linear history: Much neater and easier to follow.
  • Ideal for feature branch integration: Your changes appear as if they were made upon the latest commit of the base.
  • Easier to review and revert: Fewer merge commits to parse.

Cons:

  • Rewrites history: This can be dangerous if others are sharing the branch — their history will diverge.
  • Potential for conflicts: During the rebase, you might have to resolve conflicts multiple times if they’re present in many commits.
  • Discouraged on public branches: Only use rebase on local or personal branches.

Key Differences

Feature Merge Rebase
History Non-linear, with explicit merge commits Linear, as if work was developed after the latest base
Commit IDs Preserves original commit IDs Rewrites commit history (new commit IDs)
Collaboration Safe on shared/public branches Dangerous on shared/public branches
Conflict Handling Resolves all conflicts in a single merge commit May require repeated conflict resolution per commit
Clarity Shows branch structure and merge points Cleaner, but may hide the original context
Use Case Integrating long-lived branches, collaborative workflows Local feature branch updates, tidying up before merge

When Should You Use Merge?

  • Collaborative/Public Branches: When working with others, use merge to avoid rewriting shared history.
  • Preserving Branch Context: When the origin and duration of feature development needs to be clear.
  • Complex Integration: When merging multiple branches with divergent histories.

Example:

git checkout main
git merge feature

When Should You Use Rebase?

  • Private/Local Feature Branches: Before creating a pull request or merging a feature, rebase onto the latest main to ensure up-to-date changes.
  • Cleaner History: If you want a tidy, linear project history.
  • Squashing Commits: You can use git rebase -i for interactive rebasing and squashing.

Example:

git checkout feature
git fetch origin
git rebase origin/main

Best Practices

  1. Never rebase a branch that others are working on.
  2. Use merge when collaboration and explicit branch context matter.
  3. Use rebase to keep history linear, but only on local or unpublished branches.
  4. Always check the project's contribution guidelines about preferred workflows.

Conclusion

Both git merge and git rebase are powerful tools for integrating changes in Git. The right choice depends on your workflow and collaboration needs. Merges preserve the history and branching context; rebases provide a streamlined, linear narrative. By understanding the differences and use-cases, you can keep your project history clean, collaborative, and easy to navigate.

Further Reading:

Happy coding!

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