Git Rebase vs. Git Merge
Updated on 24th Nov, 23 9.1K Views

This blog explores the topics of Git Merge and Rebase, solving their challenges and answering the important question: when to rebase when to merge, and why? Also, we will know about the workings and major differences between them.

Table of Contents:

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Overview of Git

Git is a distributed version control system widely used in software development to track and manage changes in source code. Created by Linus Torvalds, Git provides a decentralized and efficient mechanism for collaboration among developers. 

It allows multiple contributors to work on the same project simultaneously, each maintaining their own local copy of the repository. Git’s key feature is its ability to handle branching and merging seamlessly, enabling developers to create independent branches for different features or bug fixes. 

This facilitates parallel development without compromising the stability of the main codebase. Additionally, Git offers robust version tracking, enabling users to revert to previous states and manage project history effectively. Its popularity is attributed to its speed, flexibility, and support for non-linear development workflows.

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What is Git Rebase?

Git rebase is a command in Git that allows developers to modify the commit history of a branch. Unlike traditional merging, which creates additional merge commits, rebase integrates changes by moving, combining, or eliminating commits.

When a user initiates a rebase, Git temporarily saves their changes, moves to the designated base commit, applies the saved changes, and effectively replays them on top of the base. 

This results in a linear and cleaner commit history, as opposed to the potentially convoluted structure that can arise from multiple merges. 

Rebase is particularly useful for maintaining a streamlined and more readable project history, especially in situations where feature branches are frequently updated. However, caution is advised when using rebase on shared branches, as it rewrites commit history, potentially causing conflicts for collaborators.

Git Rebase

As you can see, the commits on “mybranch” have been moved to the top of the commit history. This makes the commit history more linear and easier to understand.

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How Does Git Rebase Work

Git rebase is a strong command that lets you change a branch’s commit history. A series of commits is moved or combined into a new base commit for it to function. Integrating modifications from one branch into another or clearing your commit history before merging are common use cases.

Here’s an overview of how Git rebase works:

1. Start with a Base Branch First:

Select the branch that will function as the new foundation for your modifications. Usually, you wish to update this branch with the modifications from another branch.

git checkout base_branch

2. Initiate the Rebase:

Start the rebase process, specifying the branch whose changes you want to incorporate. For example, if you’re on base_branch and want to incorporate changes from feature_branch:

git rebase feature_branch

3. Resolve Conflicts (if any):

Git may pause the rebase process if it encounters conflicts. Resolve conflicts manually by editing the conflicted files, then continue the rebase:

# After resolving conflicts
git add resolved_file
git rebase --continue

4. Repeat Step 3 if Necessary:

If there are multiple commits to apply, Git may pause at each commit for conflict resolution. Repeat the conflict resolution process until all commits are applied.

5. Complete the Rebase:

Once all commits are successfully applied, Git completes the rebase. This might involve updating the branch pointer to the new commit.

git rebase --continue

6. Switch to the Original Branch (Optional):

If you initiated the rebase from a branch other than the one you started with, switch back to that branch.

git checkout original_branch

7. Merge Changes (Optional):

If you rebase to update a feature branch, you might want to merge it back into the main branch.

git merge feature_branch

Example with Output:

Assume we have a branch named ‘feature_branch’ with changes that we want to rebase onto ‘base_branch’.

# Start with the base branch
git checkout base_branch
# Initiate the rebase
git rebase feature_branch

If conflicts arise during the rebase, Git will pause and notify you. Resolve conflicts, add the resolved files, and continue the rebase:

# After resolving conflicts
git add resolved_file
git rebase --continue

Repeat the conflict resolution process for each commit if necessary. Once the rebase is complete, you’ll be on the updated branch:

# Rebase complete
git log

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What is Git Merge?

Git merge is a command in Git used for combining changes from different branches into a single branch, typically the one currently checked out. When a merge is initiated, Git identifies the common ancestor commit of the branches involved and integrates the changes made in each branch. 

The process creates a new commit, known as a merge commit, which consolidates the changes. This allows for the synchronization of code between multiple contributors and the incorporation of features or bug fixes into a stable main branch. 

Git merge supports various strategies, including fast-forward merges and three-way merges, adapting to different collaboration scenarios. While it may introduce merge commits, making the commit history more complex, Git merge is a fundamental tool for managing code collaboration and ensuring the cohesion of development efforts.

Git Merger

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How Does Git Merge Work

Git merge is a command that combines changes from different branches in Git. Here’s a step-by-step explanation of how Git merge works:

1. Identify the Branches:

First, you need to identify the branches you want to merge. The branch you are currently on is typically referred to as the “current” or “target” branch, and the branch you want to merge into is the “source” branch.

git checkout target_branch

2. Initiate the Merge:

Once on the target branch, initiate the merge with the branch you want to merge in. This is usually done using the git merge command.

git merge source_branch

3. Find Common Ancestor:

Git identifies the common ancestor commit of the two branches. This is the point where the branches diverged.

4. Three-Way Merge:

Git performs a three-way merge, taking into account the changes made on both the source and target branches, as well as the common ancestor. This process involves comparing the three sets of changes to create a new merge commit.

5. Automatic Merging (Fast-Forward):

If the source branch has no new commits since the common ancestor, Git can perform a fast-forward merge. In this case, the target branch is simply moved to the latest commit of the source branch.

6. Resolve Conflicts (if any):

If there are conflicting changes between the branches, Git pauses the merge process and asks the user to resolve these conflicts manually. Conflicts occur when the same lines of code have been modified in different ways in the branches being merged.

# After resolving conflicts
git add resolved_file
git merge --continue

7. Commit the Merge:

After any conflicts are resolved, Git creates a new merge commit. This commit has two parent commits, representing the commit from the target branch and the commit from the source branch.

8. Completion:

The merge is now complete, and the target branch contains the changes from both branches.

git log

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Difference Between Git Rebase and Git Merge

The main difference between Git rebase and Git merge is that rebase creates a linear commit history by moving or combining commits, while merge integrates changes with the creation of new merge commits.

Here’s a tabular difference between Git Rebase and Git Merge:

FeatureGit RebaseGit Merge
Branch CleanlinessResults in a cleaner, more straightforward history.May introduce additional merge commits, leading to a potentially more complex history.
Conflict ResolutionConflicts are addressed during the reapplying of commits.Conflicts are addressed when merging divergent branches.
Base/Branch MovementMoves the entire branch to a new base commit.Leaves the base commit unchanged, creating a new merge commit.
Collaborative WorkflowSuitable for feature branches and solo development.Commonly used in collaborative workflows where feature branches are integrated into the main branch.
Project HistoryAlters the project history by rewriting commit IDs.Preserves the project history but may create a more intricate commit-graph.
Use CasesIdeal for cleaning up a feature branch before integration.Well-suited for integrating feature branches into the main development branch.

Conclusion

The particular requirements and preferences of a development workflow determine which of the two options—Git rebase or Git merge—to choose. Git rebase is perfect for solo developers or those looking for a clean feature branch integration because it provides a simplified and linear commit history by rewriting commits. Rebasing shared branches, however, requires care to prevent destroying cooperation and creating disputes. Git merge, on the other hand, uses merge commits to incorporate changes while maintaining the commit history. When working on collaborative projects, this method works well when a more thorough history and traceability of feature branch integrations are required. In the end, the choice should take into account elements like workflow preferences, cooperation requirements, and project cleanliness.

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