# Partial Clone

As Git repositories grow in size, they can become cumbersome to work with
because of the large amount of history that must be downloaded, and the large
amount of disk space they require.

[Partial clone](https://github.com/git/git/blob/master/Documentation/technical/partial-clone.txt)
is a performance optimization that "allows Git to function without having a
complete copy of the repository. The goal of this work is to allow Git better
handle extremely large repositories."

Git 2.22.0 or later is required.

## Filter by file size

> [Introduced](https://gitlab.com/gitlab-org/gitaly/-/issues/2553) in GitLab 12.10.

Storing large binary files in Git is normally discouraged, because every large
file added will be downloaded by everyone who clones or fetches changes
thereafter. This is slow, if not a complete obstruction when working from a slow
or unreliable internet connection.

Using partial clone with a file size filter solves this problem, by excluding
troublesome large files from clones and fetches. When Git encounters a missing
file, it will be downloaded on demand.

When cloning a repository, use the `--filter=blob:limit=<size>` argument. For example,
to clone the repository excluding files larger than 1 megabyte:

```shell
git clone --filter=blob:limit=1m git@gitlab.com:gitlab-com/www-gitlab-com.git
```

This would produce the following output:

```plaintext
Cloning into 'www-gitlab-com'...
remote: Enumerating objects: 832467, done.
remote: Counting objects: 100% (832467/832467), done.
remote: Compressing objects: 100% (207226/207226), done.
remote: Total 832467 (delta 585563), reused 826624 (delta 580099), pack-reused 0
Receiving objects: 100% (832467/832467), 2.34 GiB | 5.05 MiB/s, done.
Resolving deltas: 100% (585563/585563), done.
remote: Enumerating objects: 146, done.
remote: Counting objects: 100% (146/146), done.
remote: Compressing objects: 100% (138/138), done.
remote: Total 146 (delta 8), reused 144 (delta 8), pack-reused 0
Receiving objects: 100% (146/146), 471.45 MiB | 4.60 MiB/s, done.
Resolving deltas: 100% (8/8), done.
Updating files: 100% (13008/13008), done.
Filtering content: 100% (3/3), 131.24 MiB | 4.65 MiB/s, done.
```

The output will be longer because Git will first clone the repository excluding
files larger than 1 megabyte, and second download any missing large files needed
to checkout the `master` branch.

When changing branches, Git may need to download more missing files.

## Filter by object type

> [Introduced](https://gitlab.com/gitlab-org/gitaly/-/issues/2553) in GitLab 12.10.

For enormous repositories with millions of files, and long history, it may be
helpful to exclude all files and use in combination with `sparse-checkout` to
reduce the size of your working copy.

```plaintext
# Clone the repo excluding all files
$ git clone --filter=blob:none --sparse git@gitlab.com:gitlab-com/www-gitlab-com.git
Cloning into 'www-gitlab-com'...
remote: Enumerating objects: 678296, done.
remote: Counting objects: 100% (678296/678296), done.
remote: Compressing objects: 100% (165915/165915), done.
remote: Total 678296 (delta 472342), reused 673292 (delta 467476), pack-reused 0
Receiving objects: 100% (678296/678296), 81.06 MiB | 5.74 MiB/s, done.
Resolving deltas: 100% (472342/472342), done.
remote: Enumerating objects: 28, done.
remote: Counting objects: 100% (28/28), done.
remote: Compressing objects: 100% (25/25), done.
remote: Total 28 (delta 0), reused 12 (delta 0), pack-reused 0
Receiving objects: 100% (28/28), 140.29 KiB | 341.00 KiB/s, done.
Updating files: 100% (28/28), done.

$ cd www-gitlab-com

$ git sparse-checkout init --cone

$ git sparse-checkout add data
remote: Enumerating objects: 301, done.
remote: Counting objects: 100% (301/301), done.
remote: Compressing objects: 100% (292/292), done.
remote: Total 301 (delta 16), reused 102 (delta 9), pack-reused 0
Receiving objects: 100% (301/301), 1.15 MiB | 608.00 KiB/s, done.
Resolving deltas: 100% (16/16), done.
Updating files: 100% (302/302), done.
```

For more details, see the Git documentation for
[`sparse-checkout`](https://git-scm.com/docs/git-sparse-checkout).

## Filter by file path

CAUTION: **Experimental:**
Partial Clone using `sparse` filters is experimental, slow, and will
significantly increase Gitaly resource utilization when cloning and fetching.

Deeper integration between Partial Clone and Sparse Checkout is being explored
through the `--filter=sparse:oid=<blob-ish>` filter spec, but this is highly
experimental. This mode of filtering uses a format similar to a `.gitignore`
file to specify which files should be included when cloning and fetching.

For more details, see the Git documentation for
[`rev-list-options`](https://gitlab.com/gitlab-org/git/-/blob/9fadedd637b312089337d73c3ed8447e9f0aa775/Documentation/rev-list-options.txt#L735-780).

With the `uploadpack.allowFilter` and `uploadpack.allowAnySHA1InWant` options
enabled on the Git server:

1. **Create a filter spec.** For example, consider a monolithic repository with
   many applications, each in a different subdirectory in the root. Create a file
   `shiny-app/.filterspec` using the GitLab web interface:

   ```plaintext
   # Only the paths listed in the file will be downloaded when performing a
   # partial clone using `--filter=sparse:oid=shiny-app/.gitfilterspec`

   # Explicitly include filterspec needed to configure sparse checkout with
   # git config --local core.sparsecheckout true
   # git show master:snazzy-app/.gitfilterspec >> .git/info/sparse-checkout
   shiny-app/.gitfilterspec

   # Shiny App
   shiny-app/

   # Dependencies
   shimmery-app/
   shared-component-a/
   shared-component-b/
   ```

1. **Create a new Git repository and fetch.** Support for `--filter=sparse:oid`
   using the clone command is incomplete, so we will emulate the clone command
   by hand, using `git init` and `git fetch`. Follow
   [issue tracking support for `--filter=sparse:oid`](https://gitlab.com/gitlab-org/git/issues/4)
   for updates.

   ```shell
   # Create a new directory for the Git repository
   mkdir jumbo-repo && cd jumbo-repo

   # Initialize a new Git repository
   git init

   # Add the remote
   git remote add origin <url>

   # Enable partial clone support for the remote
   git config --local extensions.partialClone origin

   # Fetch the filtered set of objects using the filterspec stored on the
   # server. WARNING: this step is slow!
   git fetch --filter=sparse:oid=master:shiny-app/.gitfilterspec origin

   # Optional: observe there are missing objects that we have not fetched
   git rev-list --all --quiet --objects --missing=print | wc -l
   ```

   CAUTION: **IDE and Shell integrations:**
   Git integrations with `bash`, `zsh`, etc and editors that automatically
   show Git status information often run `git fetch` which will fetch the
   entire repository. You many need to disable or reconfigure these
   integrations.

1. **Sparse checkout** must be enabled and configured to prevent objects from
   other paths being downloaded automatically when checking out branches. Follow
   [issue proposing automating sparse checkouts](https://gitlab.com/gitlab-org/git/issues/5) for updates.

   ```shell
   # Enable sparse checkout
   git config --local core.sparsecheckout true

   # Configure sparse checkout
   git show master:snazzy-app/.gitfilterspec >> .git/info/sparse-checkout

   # Checkout master
   git checkout master
   ```
