What is Three Way Merge in Git: Simple Explanation and Example

A three way merge in Git is a method to combine changes from two branches by comparing their latest commits with their common ancestor. It uses three points: the base (common ancestor), and the two branch tips, to automatically merge changes and resolve conflicts if any.

How It Works

Imagine you and a friend start writing a story from the same original draft. Later, you both make changes separately. To combine your edits, you look at the original draft and both your versions. This is what a three way merge does in Git.

Git finds the common starting point (called the base), then compares it with the two versions you want to merge. It looks for changes made in each branch since that base. If the changes don't overlap, Git merges them automatically. If there are conflicts, Git asks you to decide which changes to keep.

Example

This example shows a simple three way merge between two branches named feature and main.

bash

git checkout main
# Make some changes and commit

git checkout -b feature
# Make different changes and commit

git checkout main

# Merge feature branch into main using three way merge
git merge feature

Output

Updating abc1234..def5678
Fast-forward
 file.txt | 2 ++
 1 file changed, 2 insertions(+)

When to Use

Use a three way merge when you want to combine changes from two branches that have diverged from a common point. This happens often when multiple people work on the same project in parallel.

It helps keep work organized and integrated without losing anyone's changes. For example, merging a feature branch back into the main branch after development is done uses a three way merge.

Key Points

• Three way merge uses the common ancestor and two branch tips to merge changes.
• It can automatically merge non-conflicting changes.
• Conflicts require manual resolution.
• It is the default merge method in Git.

Key Takeaways

Three way merge compares the base and two branch tips to combine changes.

It automatically merges when changes do not conflict.

Conflicts during merge need manual fixing.

It is commonly used to merge feature branches into main branches.

Understanding three way merge helps manage parallel work in Git.