Rebase vs merge mental model in Git - Visual Side-by-Side Comparison

Process Flow - Rebase vs merge mental model

Start: Branch A and Branch B diverged

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Option 1: Merge

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Create a new merge commit

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Branches combined with history preserved

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End

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Option 2: Rebase

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Move Branch B commits on top of Branch A

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Rewrite Branch B history

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Linear history without merge commit

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End

Shows two ways to combine branches: merge creates a new commit joining histories, rebase moves commits to create a straight line.

Execution Sample

Git

git checkout feature
# Option 1: git merge main
# Option 2: git rebase main

Switch to feature branch, then either merge main into it or rebase feature onto main.

Process Table

Step	Action	Branch State Before	Branch State After	Result
1	Start with main and feature branches diverged	main: A-B-C feature: A-B-D-E	main: A-B-C feature: A-B-D-E	Branches diverged at commit B
2	Merge main into feature	feature: A-B-D-E	feature: A-B-D-E-M	New merge commit M combines C and E
3	Feature branch now has merge commit	feature: A-B-D-E-M	feature: A-B-D-E-M	History shows branching and merging
4	Reset feature branch to before merge	feature: A-B-D-E-M	feature: A-B-D-E	Prepare for rebase
5	Rebase feature onto main	feature: A-B-D-E	feature: A-B-C-D'-E'	Commits D and E replayed on top of C as D' and E'
6	Feature branch has linear history	feature: A-B-C-D'-E'	feature: A-B-C-D'-E'	No merge commit, history looks like a straight line
7	End	feature: A-B-C-D'-E'	feature: A-B-C-D'-E'	Branches combined by rebase or merge

💡 Execution stops after feature branch is updated by merge or rebase.

Status Tracker

Variable	Start	After 2 (merge)	After 5 (rebase)	Final
feature branch commits	A-B-D-E	A-B-D-E-M	A-B-C-D'-E'	A-B-C-D'-E'

Key Moments - 3 Insights

Why does merge create a new commit but rebase does not?

Merge combines histories by creating a new commit (row 2), while rebase moves commits to a new base, rewriting history without a merge commit (row 5).

What does it mean that rebase rewrites history?

Rebase creates new commits (D' and E') with the same changes but different parent commits, making history linear (row 5), unlike merge which preserves original commits.

When should I prefer merge over rebase?

Use merge to keep full history and show branch structure (row 3). Use rebase to keep history clean and linear (row 6).

Visual Quiz - 3 Questions

Look at the execution table, what is the feature branch state after step 2?

A A-B-D-E-M (with a merge commit)

B A-B-C-D'-E' (rebased commits)

C A-B-D-E (unchanged)

D A-B-C (main branch only)

💡 Hint

Check the 'Branch State After' column at step 2 in the execution table.

At which step does the feature branch history become linear?

A Step 2

B Step 5

C Step 3

D Step 1

💡 Hint

Look for when commits D and E are replayed on top of C as D' and E' in the execution table.

If you want to keep the branch history showing all merges, which command would you use?

A git rebase main

B git merge main

C git reset main

D git checkout main

💡 Hint

Refer to the action in step 2 where a merge commit is created.

Concept Snapshot

Rebase vs Merge in Git:
- Merge combines branches by creating a new commit.
- Rebase moves commits to a new base, rewriting history.
- Merge preserves branch history and shows merges.
- Rebase creates a linear history without merge commits.
- Use merge for shared branches, rebase for clean history.

Full Transcript

This visual shows how Git combines branches using merge or rebase. Initially, main and feature branches diverge at commit B. Using merge, a new commit M joins the histories, preserving the branch structure. Using rebase, commits from feature are moved on top of main's latest commit C, creating new commits D' and E' and a straight history line. Merge keeps all commits and shows the branch split and join. Rebase rewrites commits to make history linear without merge commits. Choose merge to keep full history or rebase to keep history clean.

Practice

1. What is the main difference between git merge and git rebase?

easy

A. git merge rewrites commit messages; git rebase preserves commit messages.

B. git merge deletes the source branch; git rebase deletes the target branch.

C. git merge only works on remote branches; git rebase only works on local branches.

D. git merge combines histories preserving all commits; git rebase rewrites history to create a linear sequence.

Solution

1. Step 1: Understand git merge behavior

   git merge combines two branches by creating a new commit that preserves the history of both branches without changing existing commits.

2. Step 2: Understand git rebase behavior

   git rebase moves or reapplies commits from one branch onto another, rewriting history to make it look like a straight line.

3. Final Answer:

   git merge combines histories preserving all commits; git rebase rewrites history to create a linear sequence. -> Option D

4. Quick Check:

   Merge preserves history, rebase rewrites it [OK]

Hint: Merge keeps history; rebase rewrites it linearly [OK]

Common Mistakes:

• Thinking merge deletes branches
• Believing rebase only works on remote branches
• Confusing which command rewrites history

2. Which of the following is the correct syntax to rebase the current branch onto main?

easy

A. git rebase main

B. git merge main

C. git rebase origin/main

D. git checkout main && git rebase

Solution

1. Step 1: Identify the command to rebase current branch

   The command git rebase main rebases the current branch onto the main branch.

2. Step 2: Check other options for correctness

   git merge main merges, not rebases; git rebase origin/main rebases onto remote tracking branch which may be outdated; git checkout main && git rebase is invalid syntax.

3. Final Answer:

   git rebase main -> Option A

4. Quick Check:

   Rebase current branch onto main = git rebase main [OK]

Hint: Use 'git rebase branch-name' to rebase current branch [OK]

Common Mistakes:

• Using merge instead of rebase
• Rebasing onto remote branch without fetching
• Incorrect chaining of commands

3. Given the following commands executed in order on branch feature:

git checkout feature
git rebase main
git log --oneline --graph

What will the commit history look like compared to using git merge main instead?

medium

A. A linear history with feature commits on top of main commits.

B. A merge commit combining main and feature histories.

C. No change in history; feature branch remains separate.

D. Feature branch commits are deleted.

Solution

1. Step 1: Understand effect of git rebase main on feature branch

   Rebasing moves feature commits to be based on the latest main commits, creating a straight, linear history.

2. Step 2: Compare with git merge main effect

   Merging creates a new merge commit that combines histories, preserving the branch structure and showing a branch point.

3. Final Answer:

   A linear history with feature commits on top of main commits. -> Option A

4. Quick Check:

   Rebase = linear history; merge = merge commit [OK]

Hint: Rebase = linear history; merge = merge commit [OK]

Common Mistakes:

• Thinking rebase creates merge commits
• Believing history stays unchanged after rebase
• Assuming commits are deleted after rebase

4. You ran git rebase main on your feature branch but got conflicts. After resolving conflicts, which command should you run to continue the rebase?

medium

A. git commit -m 'resolved conflicts'

B. git merge --continue

C. git rebase --continue

D. git rebase --abort

Solution

1. Step 1: Identify the correct command to continue rebase after conflicts

   After resolving conflicts during a rebase, git rebase --continue tells Git to proceed with applying remaining commits.

2. Step 2: Understand other options

   git merge --continue is for merge conflicts, not rebase; git commit -m is manual commit but rebase expects --continue; git rebase --abort cancels the rebase.

3. Final Answer:

   git rebase --continue -> Option C

4. Quick Check:

   Continue rebase after conflicts = git rebase --continue [OK]

Hint: Use 'git rebase --continue' after resolving conflicts [OK]

Common Mistakes:

• Using merge commands during rebase
• Trying to commit manually instead of continuing
• Aborting instead of continuing rebase

5. You want to update your feature branch with the latest changes from main but keep a clean, linear history without merge commits. Which sequence of commands achieves this safely?

hard

A. git checkout feature; git merge origin/main

B. git checkout feature; git fetch origin; git rebase origin/main

C. git checkout main; git pull; git checkout feature; git merge main

D. git checkout feature; git pull origin main

Solution

1. Step 1: Fetch latest changes from remote main branch

   git fetch origin updates local remote tracking branches without changing working branches.

2. Step 2: Rebase feature branch onto updated origin/main

   git rebase origin/main reapplies feature commits on top of latest main commits, keeping history linear and clean.

3. Final Answer:

   git checkout feature; git fetch origin; git rebase origin/main -> Option B

4. Quick Check:

   Fetch then rebase for clean update [OK]

Hint: Fetch first, then rebase onto remote main for clean history [OK]

Common Mistakes:

• Merging instead of rebasing for linear history
• Pulling directly on feature branch causing merge commits
• Not fetching latest remote changes before rebase