Introduction

In the Git version control system, cloning repositories is a fundamental operation. However, there are various flags and options available to customize the cloning process according to specific needs. Two such options are --shared and --reference, each serving different purposes with some similar underlying mechanics but intended for distinct scenarios. Understanding these differences helps optimize workflows, especially when dealing with large repositories or constrained storage.

Git Clone Basics

When you run the git clone command, Git copies an existing repository from a remote or local source to a new local directory. By default, this involves fetching every object in the repository's history, which can be storage intensive and time-consuming if the repository is large.

Git Clone with --shared

The --shared option is used when you want to clone a repository in a way that shared objects are accessible from the same database, meaning the local copy does not have its standalone .git directory. Instead, it uses the objects from another repository.

Technical Explanation

• Use case: Usually limited to scenarios where you want to conserve space and are comfortable with the cloned repository sharing the object database with the source.
• Repository structure: The newly cloned repository does not house its objects within a .git/objects directory. Instead, it references the object directory of the source repository.
• Behavior: Modifying objects will affect all other repositories sharing that database. This means it's not suitable for situations where you need full autonomy or intend to modify the history.

Example

Assume you have a source repository at /path/to/source_repo. Cloning it with shared objects would look like this:

• Use case: Ideal when you want to conserve bandwidth and space while still wanting some level of independence from the original repository.
• Repository structure: The cloned repository has its own .git/objects directory, but initially populates it by linking objects from the reference repository.
• Behavior: The new clone can fetch new objects independently of the reference repository. Only objects present at cloning are hard links.