Git is an open-source version control system many developers rely on for source code management. It has many features that can make life easier for DevOps practitioners. Today we’re talking about two specific commands: Git rebase and Git merge.
This article defines both Git rebase and merge, how they work, and how they’re similar and different. We will also look at each option’s pros and cons, strategies, and how they can be used together. Furthermore, we’ll look at a Git rebase example and touch on other related topics such as Git reset and a squash and merge vs. rebase and merge comparison.
Let’s kick things off with some basic definitions.
- Commit: In terms of Git, a commit is the location that stores the code and any changes made to it. For example, if a developer saves three Java files on Git, they are grouped into one commit and assigned an ID number. If the developer later change the code and adds one more Java file, these changes are saved as another commit with a different ID number. Anytime someone makes a change in Git, it generates a new commit.
- Branch: A branch represents different isolated versions of a code. For instance, a programmer wants to add new features to a website. The website’s code is stored by default on the master branch. However, the programmer wants to tinker with the website code and add the new features without altering the website’s existing code. So, they create a new branch from the master branch, which contains a copy of the master branch’s code. Now the programmer can experiment and make changes, and once the work is done, they merge the changes of the feature branch into the original master branch.
The programmer needs to perform a merge, which brings us to our original point: the difference between a Git rebase, and a Git merge.
Now let’s define these two different approaches — Git Rebase vs. Merge.
What Is Git Rebase?
Git rebase is a command that lets users integrate changes from one branch to another, and the logs are modified once the action is complete. Git rebase was developed to overcome merging’s shortcomings, specifically regarding logs.
What Is Git Merge?
Git merge is a command that allows developers to merge Git branches while the logs of commits on branches remain intact.
The merge wording can be confusing because we have two methods of merging branches, and one of those ways is actually called “merge,” even though both procedures do essentially the same thing.
In summary, here’s an image that shows an initial branch, a Git rebase, and a Git merge.
The Workings of Git Rebase and Merge
Git rebase takes all the changes, and compresses them into a single patch and integrates this new patch onto the target branch. Then, it moves the completed work from one branch to another, typically the master branch. In the process, rebase flattens the history, removing unwanted entries.
Git merge, on the other hand, only changes the target branch and creates a commit, preserving the history of the source branch.
Git Rebase and Git Merge Similarities
Both the rebase and merge commands exist for the same reason: they combine the work of multiple developers into a single entity, integrating changes between branches. That about sums up their similarities. On the other hand, their differences are considerably more profound.
What’s the Difference Between Merge and Rebase?
A head-to-head comparison chart is the best way to illustrate the differences between Git merge and Git rebase.
Merge lets you merge different Git branches.
Rebase allows you to integrate the changes from one branch into another.
Merge logs show you the complete history of commit merging.
Rebase logs are linear. As the commits are rebased, the history is altered to reflect this.
All the commits on a feature branch are combined into a single commit on the master branch.
All commits are rebased, and the same number of commits are added to the master branch.
Merge is best used when the target branch is supposed to be shared.
Rebase is best used when the target branch is private.
Merge preserves history.
Rebase rewrites history.
The Advantages and Disadvantages of Git Rebase and Git Merge
Each merge process brings plusses and minuses to the table.
Git Merge Benefits
- Merge is simple, straightforward, and familiar
- Merge preserves the entire history in chronological order
- Merge maintains the branch’s context
- Merge creates a complete log that helps developers understand the big picture, showing when and how each merge occurred
- Merge makes it easy for users to find mistakes and correct them
Git Merge Drawbacks
- Merge isn’t very user-friendly
- Merge’s exhaustive nature results in a clumsy history and log
- Merge’s git log must be constantly and properly maintained, or devolve into a mess
Git Rebase Benefits
- Rebase streamlines a possibly complex history
- Rebase cleans up intermediate commits by turning them into a single commit, making life easier for DevOps teams
- Rebase avoids the merge commit noise typically found in busy repos and busy branches
- Rebase creates a streamlined, linear log
- Rebase provides a lack of clutter, which facilitates project movement
Git Rebase Drawbacks
- Users can’t track how and when commits were merged on the target branch
- Rebase won’t work with pull requests since you can’t see minor changes someone else made
- Rebase makes you resolve conflicts in the order they were created to continue the rebase. Unfortunately, this means more work for you, as you may need to fix the same conflicts repeatedly
- Rebase lowers the feature down to a small number of commits, making it challenging to see the context
Git Rebase vs. Merge Strategies
Your branching strategy must factor in the roles, goals, and shape of your organization. After all, Git merge and Git rebase are viable merging strategies (more on that later). In addition, you must consider factors such as your organization/team's Git competence and level of rebase.
What matters more to your team? Is it the simplicity of rebasing or the history and traceability of merging? An effective merging strategy relies on comparing team needs against available resources.
How Do You Use Git Rebase and Git Merge Together?
It’s possible to use both Git rebase and Git merge in the same project. For example, you can work on a feature branch, create another feature branch off it, make your changes, and finalize them as commits. You could then Git merge both feature branches, then use a Git rebase to merge the feature branches into the main branch. This way, you, as the developer, can do you work on a feature branch, but other team members won’t see it when they look at the main branch.
Put another way; you can use Git rebase to work on a private branch, then do Git merge to bring everything together into one coherent timeline.
What’s a Git Reset?
Git reset is a powerful command that undoes changes, moving the repository back to a previous commit, and eliminating any changes made after the commit. It’s literally hitting the “reset” button, undoing local changes.
What’s the Difference Between Squash and Merge, and Rebase and Merge?
A squash and merge works best when you have too many commits on a single feature, and not all are useful anymore, so you combine them onto the master as a single commit. This approach is different from a rebase and merge, where you take a feature branch and attach it to the master.
Thus, the squash and merge keep the changes but removes the individual commits from the history. The rebase and merge move the entire branch and rewrites the history to reflect this.
Rebase vs. Merge. Which is Better?
Like so many other head-to-head comparisons of products, services, and strategies, the answer depends on your specific situation and needs. For example, both Git rebase and Git merge are good merging strategies, but each shine in a different way and under other circumstances.
If you’re working either on a small team or by yourself, Git rebase is a better choice. However, if you're working in a big group, you want to use Git merge.
The choice boils down to how transparent and accessible you want the logs to be.
Looking at a Git Rebase Example
This illustration, provided by Gcapes.github, shows a good example of a Git rebase.
As we can see, the master branch has three commits and a feature branch which in turn has two commits. The master branch commits are labeled 1, 2, and 3. The feature branch commits are labeled A and B. The developer works on the feature branch, makes the needed changes, and decides to merge the branches using Git rebase.
So, the feature branch gets tacked onto the original branch, creating new commits for each commit in the master branch. Finally, the feature branch is gone, and its commits are renamed 4 and 5, tacked on to the master branch, and become part of the commit number sequence.
A Git rebase is just another way of saying, “Please add my changes to the work that has already been done.”
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