Understanding Merge Types

Advanced Git

Amanda Crawford-Adamo

Software and Data Engineer

I'm Amanda

A picture of Amanda

What is git merge?

Git Merge Command:

git merge

Combines changes from one branch into another
Finds the common base between two branches
Use different merge strategies

Road where two roads join with two cars intersecting on the same road

Fast-forward merge

What is fast forward merge?

Keep a simple, straight history
Ideal for short-lived branches with simple changes

When not to use

Need to preserve branch history
Complex feature development in long-lived branches
Merge conflict between branches - fast forward fails immediately!

Fast-forward merge (before)

A graph that shows to branches: main and feature branch. Main has two commits. Feature branch diverges after main latest commit with an additional commit in it's branch.

Fast-forward merge syntax

Git Merge Fast Forward Default

git checkout main
git merge feature_branch

Force Git Merge Fast Forward

git merge <branch> --ff-only

Example

git checkout main
git merge feature_branch --ff-only

Fast-forward merge (after)

A graph that shows to branches: main and feature branch. Main has three commits. Feature branch diverges after main second commit with an additional commit in it's branch. Main's third commit is a copy of feature branch's latest commit.

Recursive merge

What is a recursive merge?

Creates a merge commit with two parents
Preserve the entire project history
Ideal for long-lived branches
Maintain branching structure

When not to use

When you want to maintain a simple and linear history
Quick and minor changes

Recursive merge (before)

A graph that shows to branches: main and feature branch. Main has three commits. Feature branch diverges after main first commit with an additional two commit in it's branch.

Recursive merge syntax

Recursive Merge Command:

git merge --no-ff <branch>

Example

$ git checkout main
Switched to branch 'main'
Your branch is up to date with 'origin/main'.

$ git merge --no-ff feature_branch
Merge made by the 'recursive' strategy.
...

Recursive merge (after)

Summary

Fast forward merges keeps history simple and linear
Recursive merges preserves historical context
Recursive merges are better for more complex development

Fast Forward Merge Commands

git merge <branch_name> # default command
git merge --ff-only <branch_name> # force fast forward merge

Recursive Merge Command

git merge --no-ff <branch_name>

Let's practice!

Advanced Git