Fast-forward merge in Git - Step-by-Step Execution

Process Flow - Fast-forward merge

Start on main branch

↓

Create feature branch

↓

Make commits on feature branch

↓

Switch back to main branch

↓

Check if main is behind feature

Yes↓

Fast-forward merge: move main pointer to feature

↓

Main branch updated, no merge commit

↓

End

This flow shows how a fast-forward merge moves the main branch pointer forward to the feature branch commit when no divergent commits exist.

Execution Sample

Git

git checkout main

git checkout -b feature

git commit -m "Add feature"

git checkout main

git merge feature

This sequence creates a feature branch, commits to it, then merges it back into main using fast-forward.

Process Table

Step	Command	Branch HEAD	Action	Result
1	git checkout main	main	Switch to main branch	HEAD points to main branch tip
2	git checkout -b feature	feature	Create and switch to feature branch	feature branch created at main tip, HEAD points to feature
3	git commit -m "Add feature"	feature	Commit on feature branch	feature branch moves forward by one commit
4	git checkout main	main	Switch back to main branch	HEAD points to main branch tip (behind feature)
5	git merge feature	main	Fast-forward merge	main branch pointer moves to feature commit, no merge commit created

💡 Fast-forward merge completes because main branch has no new commits since feature branch was created.

Status Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5
HEAD	main	main	feature	feature	main	main
main branch pointer	commit0	commit0	commit0	commit0	commit0	commit1 (feature commit)
feature branch pointer	commit0	commit0	commit1	commit1	commit1	commit1

Key Moments - 3 Insights

Why does the merge not create a new commit?

Because main branch has no new commits after branching, git just moves main pointer forward to feature commit (see execution_table step 5).

What happens if main had new commits after feature branch was created?

Fast-forward merge would not be possible; git would create a merge commit to combine histories.

Does fast-forward merge change the commit history?

No, it only moves the branch pointer forward without creating new commits, preserving a linear history.

Visual Quiz - 3 Questions

Look at the execution table, what is the branch HEAD after step 3?

A feature

B main

C detached HEAD

D unknown

💡 Hint

Check the 'Branch HEAD' column at step 3 in the execution_table.

At which step does the main branch pointer move to the feature commit?

A Step 3

B Step 4

C Step 5

D It never moves

💡 Hint

Look at the 'Result' column in execution_table for when main branch pointer updates.

If main had new commits after branching, what would change in the execution table?

A HEAD would point to detached state

B Step 5 would create a merge commit instead of fast-forward

C Step 3 would fail

D Feature branch would be deleted

💡 Hint

Refer to key_moments about when fast-forward merge is possible.

Concept Snapshot

Fast-forward merge moves the branch pointer forward when no divergent commits exist.
Syntax: git merge <branch>
If main is behind feature, main pointer moves to feature commit.
No merge commit is created.
Preserves linear history.
Only works if main has no new commits since branching.

Full Transcript

Fast-forward merge happens when you merge a branch that is ahead of your current branch without any new commits on the current branch. You start on main, create a feature branch, make commits there, then switch back to main. When you run git merge feature, git moves the main branch pointer forward to the feature commit because main has no new commits. This merge does not create a new commit, keeping history linear. If main had new commits, git would create a merge commit instead. This process is simple and keeps your commit history clean.