Rebasing & Merging

Two ways of solving the same problem

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The Problem

Suppose you started working on a new feature in a dedicated branch meanwhile another team member updates the main branch with new commits. This results in a forked history, which should be familiar to anyone who has used Git as a collaboration tool.

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You may want to integrate them into your feature branch. You can either rebase or merge.

The Solution

1. Merging

The easiest option is to merge the main branch into the feature branch using the commands:

git checkout feature
git merge main

The above merge process will create a new merge commit in the feature branch which will have a history of both branches.

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Pros

  • It’s a very simple Git methodology to use and understand.
  • The existing commits on both branches remain untouched. It preserves the commit history.

Cons

  • Whenever git merge is run, an extra merge commit is created. And if the main branch is very active, this can pollute your feature branch’s history quite a bit. While it’s possible to mitigate this issue with advanced git log options, it can make it hard for other developers to understand the history of the project. One way to avoid the merge commit is to use git rebase instead.

2. Rebasing

You can instead rebase the feature branch onto the main branch using the commands:

git checkout feature
git rebase main

This moves the entire feature branch so that it begins at the tip of the main branch. All of the work is still there, but you have re-written history.

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Instead of creating a merge commit in the feature branch, rebasing re-writes the commit history by creating brand new commits for each commit in the feature branch.

Pros

  • Rebasing eliminates the unnecessary merge commits required by git merge resulting in cleaner project history.

  • It also results in a perfectly linear project history—you can follow the tip of the feature all the way to the beginning of the project without any forks.

Cons

  • Rebasing is a very powerful feature. That being said, it is risky as well if it is not used in the right way. Never use it on public branches. For example, think about what would happen if you rebased main onto your feature branch:

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Now, you are referring to a new main branch and everybody else’s referring to the old main branch. The only way to synchronize the two main branches is to merge them back together, resulting in an extra merge commit and two sets of commits that contain the same changes (the original ones, and the ones from your rebased branch). Needless to say, this is a very confusing situation.

Summary

  • If you would prefer a clean, linear project history free of unnecessary merge commits, you should go for git rebase.

  • If you want to preserve the complete history of your project and avoid the risk of re-writing public commits, you can stick with git merge.

References

That’s all for this article. Thank you for reading it.

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