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Shrinking a Git Repository

Origin of the information or article on a web-archive since it no longer available.
Also see "BFG Repo-Cleaner".

Deep Clone the Repository

If you don't already have a local clone of the repository in question, create one now: 

git clone remote-url

Now — you may have cloned the repository, but you don't have all the remote branches. This is imperative to ensure a proper 'deep clean'. To do this, we'll need a little Bash script:

#!/bin/bash
for branch in `git branch -a | grep remotes | grep -v HEAD | grep -v master`; do
git branch --track ${branch##*/} $branch
done

Copy this code into a file, chmod +x filename.sh, and then execute it with ./filename.sh. You will now have all the remote branches as well (it's a shame Git doesn't provide this functionality).

Discovering the large files

Credit is due to Antony Stubbs here - his Bash script identifies the largest files in a local Git repository, and is reproduced verbatim below:

#!/bin/bash
#set -x 

# Shows you the largest objects in your repo's pack file.
# Written for osx.
#
# @see http://stubbisms.wordpress.com/2009/07/10/git-script-to-show-largest-pack-objects-and-trim-your-waist-line/
# @author Antony Stubbs

# set the internal field spereator to line break, so that we can iterate easily over the verify-pack output
IFS=$'\n';

# list all objects including their size, sort by size, take top 10
objects=`git verify-pack -v .git/objects/pack/pack-*.idx | grep -v chain | sort -k3nr | head`

echo "All sizes are in kB. The pack column is the size of the object, compressed, inside the pack file."

output="size,pack,SHA,location"
for y in $objects
do
    # extract the size in bytes
    size=$((`echo $y | cut -f 5 -d ' '`/1024))
    # extract the compressed size in bytes
    compressedSize=$((`echo $y | cut -f 6 -d ' '`/1024))
    # extract the SHA
    sha=`echo $y | cut -f 1 -d ' '`
    # find the objects location in the repository tree
    other=`git rev-list --all --objects | grep $sha`
    #lineBreak=`echo -e "\n"`
    output="${output}\n${size},${compressedSize},${other}"
done

echo -e $output | column -t -s ', '

Execute this script as before, and you'll see some output similar to the below:

All sizes are in kB. The pack column is the size of the object, compressed, inside the pack file.
size     pack    SHA                                       location
1111686  132987  a561d25105c79aa4921fb742745de0e791483afa  08-05-2012.sql
5002     392     e501b79448b9e970ab89b048b3218c2853fdfc88  foo.sql
266      249     73fa731bb90b04dcf79eeea8fdd637ba7df4c089  app/assets/images/fw/iphone.fw.png
265      43      939b31c563bd40b1ca70e4f4a9f7d67c27c936c0  doc/models_complete.svg
247      39      03514d9e84418573f26b205bae7e4e57057c036f  unprocessed_email_replies.sql
193      49      6e601c4067aaddb26991c4bd5fbddef003800e70  public/assets/jquery-ui.min-0424e108178defa1cc794ee24fc92d24.js
178      30      c014b20b6fed9f17a0b2809ac410d74f291da26e  foo.sql
158      158     15f9e56bc0865f4f303deff053e21909661a716b  app/assets/images/iphone.png
103      36      3135e15c5cec75a4c85a0636b154b83221020c97  public/assets/application-c65733a4a64a1a885b1c32694574b12a.js
99       85      c1c80bc4c09e692d5e2127e39c87ecacdb1e816f  app/assets/images/fw/lovethis_logo_sprint.fw.png

Cleaning the files

Cleaning the file will take a while, depending on how busy your repository has been.
You just need one command to begin the process:

git filter-branch --tag-name-filter cat --index-filter 'git rm -r --cached --ignore-unmatch filename' --prune-empty -f -- --all
This command is adapted from other sources — the principal addition is --tag-name-filter cat which ensures tags are rewritten as well.

After this command has finished executing, your repository should now be cleaned, with all branches and tags intact.

Reclaim space

While we may have rewritten the history of the repository, those files still exist in there, stealing disk space and generally making a nuisance of themselves.
Let's nuke the bastards:

rm -rf .git/refs/original/
git reflog expire --expire=now --all
git gc --prune=now
git gc --aggressive --prune=now

Now we have a fresh, clean repository.
In my case, it went from 180MB to 7MB.

Tell your teammates

Anyone else with a local clone of the repository will need to either use git rebase, or create a fresh clone, otherwise when they push again, those files are going to get pushed along with it and the repository will be reset to the state it was in before.