Git mental model (snapshots not diffs) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main difference between Git's mental model and traditional version control systems?

Git stores data as snapshots of the entire project at each commit, not as differences (diffs) between files.

beginner

How does Git treat files internally when you commit changes?

Git takes a snapshot of all files in the project and stores a reference to that snapshot, even if files haven't changed.

intermediate

Why is Git's snapshot model more efficient than storing diffs?

Because unchanged files are stored as links to previous snapshots, saving space and speeding up operations.

beginner

What happens if a file has not changed between commits in Git's snapshot model?

Git does not store the file again; it links to the previous snapshot of that file.

beginner

Explain the concept of a 'commit' in Git using the snapshot mental model.

A commit is like a photo capturing the entire state of your project at a moment in time.

What does Git store when you make a commit?

A Only the changes made since the last commit

B A snapshot of all files in the project

C A backup copy of the entire hard drive

D A list of file names

Git stores a snapshot of the entire project at each commit, not just the changes.

If a file hasn't changed between commits, how does Git handle it?

A Stores a new copy anyway

B Deletes the file

C Links to the previous snapshot of the file

D Marks it as deleted

Git links unchanged files to their previous snapshots to save space.

Why is Git's snapshot approach beneficial?

A It simplifies tracking project state

B It wastes disk space

C It makes commits slower

D It requires manual backups

Snapshots make it easy to see the whole project state at any commit.

Which of these best describes a Git commit?

A A list of file differences

B A temporary file

C A backup of your computer

D A snapshot of the project at a point in time

A commit is a snapshot capturing the entire project state.

Git's snapshot model means:

A Git stores the whole project state each time

B You must save every file manually

C Git stores only changes between files

D Git cannot track file history

Git stores the whole project state as snapshots, not just changes.

Describe how Git's snapshot model works compared to storing diffs.

Think of a photo album versus a list of changes.

Explain why Git's approach to storing data helps with speed and space.

Consider how reusing unchanged parts saves effort.

Practice

1. What does Git save when you run git commit?

easy

A. A backup copy of your entire computer

B. Only the changes made since the last commit

C. A list of all commands you typed

D. A snapshot of all your files at that moment

Solution

1. Step 1: Understand what git commit does

   It records the current state of your project files as a snapshot.

2. Step 2: Differentiate snapshot from changes

   Unlike some systems, Git saves the whole snapshot, not just the changes.

3. Final Answer:

   A snapshot of all your files at that moment -> Option D

4. Quick Check:

   Git saves snapshots, not diffs [OK]

Hint: Remember: Git snapshots whole files, not just changes [OK]

Common Mistakes:

• Thinking Git saves only changes (diffs)
• Confusing commit with backup
• Believing commit saves command history

2. Which of the following is the correct command to create a snapshot in Git?

easy

A. git snapshot

B. git save

C. git commit

D. git backup

Solution

1. Step 1: Recall Git commands for saving work

   The command to save a snapshot is git commit.

2. Step 2: Verify other options

   Commands like git snapshot, git save, and git backup do not exist in Git.

3. Final Answer:

   git commit -> Option C

4. Quick Check:

   git commit creates snapshots [OK]

Hint: Use git commit to save snapshots [OK]

Common Mistakes:

• Using non-existent commands like git save
• Confusing commit with backup commands
• Trying git snapshot which is invalid

3. Given this sequence of commands:

echo "Hello" > file.txt
git add file.txt
git commit -m "First snapshot"
echo "World" >> file.txt
git add file.txt
git commit -m "Second snapshot"

What does the second commit snapshot contain?

medium

A. Only the line "World" added to file.txt

B. The entire file.txt with both "Hello" and "World" lines

C. Only the line "Hello" in file.txt

D. An empty file.txt

Solution

1. Step 1: Understand what each commit saves

   Each commit saves a full snapshot of the file at that time, not just changes.

2. Step 2: Analyze the second commit content

   After appending "World", the second commit snapshot includes both "Hello" and "World" lines in file.txt.

3. Final Answer:

   The entire file.txt with both "Hello" and "World" lines -> Option B

4. Quick Check:

   Git snapshots save full file content [OK]

Hint: Each commit saves full file content, not just added lines [OK]

Common Mistakes:

• Thinking commit saves only new lines
• Confusing snapshots with diffs
• Assuming commit saves partial file

4. You ran git commit but Git says "nothing to commit, working tree clean". What is the most likely reason?

medium

A. There are no changes since the last snapshot

B. You forgot to add files with git add before commit

C. Your Git repository is corrupted

D. You need to restart your computer

Solution

1. Step 1: Understand the message meaning

   "Nothing to commit, working tree clean" means no changes are detected compared to last commit.

2. Step 2: Check if files were changed

   If no files changed, Git has no new snapshot to save, so commit does nothing.

3. Final Answer:

   There are no changes since the last snapshot -> Option A

4. Quick Check:

   No changes = no new snapshot [OK]

Hint: No changes means no new commit possible [OK]

Common Mistakes:

• Assuming you must always run git add before commit even if no changes
• Thinking repository is corrupted
• Restarting computer unnecessarily

5. You want to save your project state but only some files changed. How does Git store this when you run git commit?

hard

A. Git saves a full snapshot of all files, but reuses unchanged files from previous commits internally

B. Git saves only the changed files as diffs

C. Git saves only the changed files as full copies

D. Git saves nothing until you run git push

Solution

1. Step 1: Recall Git snapshot model

   Git saves a full snapshot of the project at commit time, not just diffs.

2. Step 2: Understand Git's storage optimization

   Internally, Git reuses unchanged files from previous commits to save space efficiently.

3. Final Answer:

   Git saves a full snapshot of all files, but reuses unchanged files from previous commits internally -> Option A

4. Quick Check:

   Snapshots with internal reuse = Git saves a full snapshot of all files, but reuses unchanged files from previous commits internally [OK]

Hint: Git snapshots all files but stores unchanged ones efficiently [OK]

Common Mistakes:

• Thinking Git saves only diffs
• Believing commit saves nothing until push
• Assuming changed files are saved as full copies only