Git Rebase Vs. Merge

Integrating code changes between branches is something developers do almost on a daily basis. With Git, you can opt for two approaches—you can either merge or you can rebase.

The main question is how do you choose between Git merge and Git rebase?

Generally speaking, merge and rebase carry out the same functions. Both are built to incorporate adjustments into one form from various divisions, so the objective is the same. But it’s the approach and process of achieving the end objective that is different for the two Git methodologies.

Read on as we explain the nuances in more detail. 

A Brief Introduction to Git

Git is an open-source version control system commonly used for source code management. It’s a revolutionary tool for developers that has various aspects, including:

  • A control system to store code and other types of content.
  • A version control system with features like branching and merging, to help users maintain a history of changes and supports when working on the same files in parallel.
  • A distributed version control system, where the code is present in two types of repositories—the local repository and the remote repository.

Next, you need to know what commit and branch mean.

  • In terms of Git, commit refers to the location where code and any other changes made to it is stored. For instance, if you save more than one Java file on Git, they’ll get grouped into one commit and assigned an ID number. If you change the code and add one more Java file later, the changes will be saved as another commit with a different ID number. 

In other words, any time someone makes a change in Git, the system will generate a new commit.

  • A branch represents different isolated versions of a code. Let us explain—suppose a programmer wants to add new features to a website, and the website’s code is generated by default on the master branch. But they don’t want to alter the existing code. 

The programmer can create a new branch from the master branch that has a copy of the master branch’s code. Once that’s done, the programmer can experiment and make changes, and once they’re satisfied with the code, merge the changes of the feature branch into the original master branch.

Now that you have a basic understanding of Git, let’s break down Git rebase vs. merge.

What is Git Merge?

A merge is a method to put a forked history back together. The git merge command lets you take independent development branches and combine them into a single branch. The interesting fact here is this command will update the current branch to reflect the merge, but the target branch will remain untouched. 

The git merge command is often used in combination with git checkout (for the selection of the current branch) and git branch -d (for deleting any obsolete source branch).

You can use git merge for combining multiple sequences of commits into a single history or to simply combine two branches. 

Advantages:

  • Straightforward and familiar method
  • Preserves the entire history in a chronological order
  • Facilitates identifying mistakes and correcting them
  • Maintains the branch context, and creates a complete log that helps devs understand the bigger picture by showing them when and how each merge took place

Disadvantages:

  • Isn’t very user-friendly
  • Exhaustive nature results in disorganized history and log
  • Git log must be properly maintained periodically or it can quickly get messy

What is Git Rebase?

A rebase is a specific approach to migrating or combining a sequence of commits to a new base commit. The git rebase command allows you to integrate changes from one branch to another, while the logs are modified once the action is complete.

This command was mainly developed to overcome shortcomings of the merge command, especially concerning logs.

Advantages:

  • Creates a streamlined linear blog 
  • Cleans up intermediate commits by transforming them into a single commit
  • Avoids the merge commit noise typically found in busy repos and branches
  • Streamlines even the most complex history
  • Facilitates more efficient and effective organization, which results in smoother project movement

Disadvantages:

  • Cannot track how and when commits were merged on the target branch
  • Isn’t compatible with pull requests as you can’t see minor changes made by someone else
  • Lowers the feature down to a small number of commits, which can make it challenging to see the context
  • Makes you resolve conflicts in the same order as they were created to continue the rebase, which can create more work for you as you may have to fix the same conflicts repeatedly

Git Rebase vs. Merge: Differences and Similarities 

To help you understand the differences and similarities between merge and rebase, here’s a point-by-point breakdown.

Differences:

  • Using the merge command, you can combine different Git branches. On the other hand, the rebase command allows you to integrate the changes from one branch into another.
  • Merge logs display the complete history of commit merging whereas reverse logs are linear. As the commits are rebased in the case of the latter, the history is altered to reflect this.
  • In case of a merge, all the commits on a feature branch can be combined into a single commit on the master branch. In the case of a rebase, all commits are rebased, which is why the same number of commits get added to the master branch.
  • The most common is the best option when you want to share the target branch, while the rebase command is more suitable for private target branches.
  • Merge preserves history whereas rebels rewrite history.

Similarities:

  • Merge and rebase combined the work of multiple developers into a single entity while integrating any changes between branches. 

In a nutshell:

  • Merge changes the target branch, followed by creating a commit—all the while preserving the history of the source branch.
  • Rebase takes all the changes and compresses them into a single patch. It follows it up by integrating the new patch onto the target branch, after which it moves the completed work from one branch to another, which is typically the master branch. In this process, rebase flattens the history, removing unwanted entries.

Git Rebase vs. Merge: When to Rebase and When to Merge?

Rebasing can create inconsistent repositories if the feature branch you’re getting changes from is shared with other devs. Therefore, git rebase isn’t recommended in this case and, instead, makes more sense for individuals.

It’s also a better method to streamline a complex history since you can then change the commit history by interactive rebase. What’s more, you can also remove undesired commits, squash two or more commits into one, or edit the commit message.

But if you want to see the history completely as it happens, merge would make a good option considering it preserves history.

Another important thing to note is that rebase will present conflicts one commit at a time. On the other hand, merge will present them all at once, which makes conflict handling easier and better. At the same time, you shouldn’t forget that reverting a rebase is more difficult than reverting a merge if there are many conflicts.

Git Rebase vs. Merge: Choosing the Right Method

When deciding between Git merge and Git rebase, you need to consider the kind of history you want.

Let’s review the facts:

Git merge is a simple Git methodology that most devs use and understand, and can help maintain the original context of the source branch. 

If one has to maintain the history graph semantically correct, then Git merge will preserve the commit history. Note that the source branch commits are separated from the other branch commits. So, it can help extract the useful feature and merge it into another branch later on.

Therefore, if you want to go for a feature-based workflow, git merge is the right choice because it helps preserve the commit history and avoids unnecessary git reverts or resets.

Git rebase is useful for maintaining a clean history. When a lot of devs work on the same branch in parallel, the history can look too intense and complicated being populated by multiple merge commits. This can result in a very messy look that can create hurdles in extracting useful information, which is something rebase can help eliminate.

So, git rebase is the better method if you want a linear history. As it keeps the changes linear and more centralized, you can avoid unnecessary commits. Nevertheless, you need to be extremely careful when applying the rebase command, because if done incorrectly, it can lead to serious consequences.

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Bryan Wise
Bryan Wise,
CIO of 6sense

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