Git Internals Deep Dive

Learning Objectives

Understand Git's object model and how it stores data
Learn about refs and how Git uses them to track branches and tags
Master the concept of packfiles and their role in Git storage
Understand Git's garbage collection process

Git's Object Model

At its core, Git is a content-addressable filesystem with a VCS user interface built on top. Understanding how Git stores and manages data helps you become a more effective Git user.

Core Objects

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Blobs:Store file contents
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Trees:Store directories and filenames
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Commits:Store metadata and project snapshots
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Tags:Store references to specific points

Object Properties

•Content-addressed using SHA-1 hash
•Immutable once created
•Compressed for storage
•Linked together in a DAG structure

Examining Git Objects

Git provides several low-level commands to examine its internal objects:

Inspecting Objects

# Show object type
$  git cat-file -t 1a410efbd13591db07496601ebc7a059dd55cfe9
 
# Show object content
$  git cat-file -p 1a410efbd13591db07496601ebc7a059dd55cfe9
 
# Show object size
$  git cat-file -s 1a410efbd13591db07496601ebc7a059dd55cfe9
 
# List objects in packfile
$  git verify-pack -v .git/objects/pack/pack-*.idx

Git References

References (refs) are pointers to commits. They're how Git keeps track of branches, tags, and other important points in your repository's history.

Types of Refs

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HEAD:Points to current branch
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Branches:Movable pointers to commits
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Tags:Fixed pointers to specific commits
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Remote refs:Track remote repository state

Working with Refs

# Show all refs
$  git show-ref
 
# Update ref
$  git update-ref refs/heads/main 1a410e
 
# Show where HEAD points
$  git symbolic-ref HEAD

Packfiles and Storage Optimization

Git uses packfiles to efficiently store objects and save space. Understanding how packfiles work helps you optimize repository performance.

Packfile Creation

# Create a packfile manually
$  git gc
 
# Force immediate packing
$  git gc --prune=now
 
# Pack a specific branch
$  git pack-objects --revs

Storage Optimizations

•Delta compression between similar objects
•Network transfer optimization
•Automatic garbage collection

Garbage Collection

Git's garbage collection process helps maintain repository health by cleaning up unnecessary files and optimizing storage.

What GC Does

•Removes unreachable objects
•Compresses similar objects
•Optimizes repository structure

GC Commands

# Run garbage collection
$  git gc
 
# Aggressive collection
$  git gc --aggressive
 
# Clean up unnecessary files
$  git prune
 
# Check what would be removed
$  git prune --dry-run

What's Next?

Now that you understand Git's internal workings, you're ready to learn about optimizing Git's performance. In the next lesson, you'll discover:

Large file handling and management
Git attributes and hooks for automation