How to remove unreferenced blobs from my git repo

How to remove unreferenced blobs from my git repo

I have a GitHub repo that had two branches – master & release.
The release branch contained binary distribution files that were contributing to a very large repo size (> 250MB), so I decided to clean things up.
First I deleted the remote release branch, via git push origin :release
Then I deleted the local release branch. First I tried git branch -d release, but git said “error: The branch ‘release’ is not an ancestor of your current HEAD.” which is true, so then I did git branch -D release to force it to be deleted.
But my repository size, both locally and on GitHub, was still huge. So then I ran through the usual list of git commands, like git gc –prune=today –aggressive, with no luck.
By following Charles Bailey’s instructions at SO 1029969 I was able to get a list of SHA1s for the biggest blobs. I then used the script from SO 460331 to find the blobs…and the five biggest don’t exist, though smaller blobs are found, so I know the script is working.
I think these blogs are the binaries from the release branch, and they somehow got left around after the delete of that branch. What’s the right way to get rid of them?

Solutions/Answers:

Solution 1:

… and without further ado, may I present to you this useful command, “git-gc-all”, guaranteed to remove all your git garbage until they might come up extra config variables:

git -c gc.reflogExpire=0 -c gc.reflogExpireUnreachable=0 -c gc.rerereresolved=0 -c gc.rerereunresolved=0 -c gc.pruneExpire=now gc

You might also need to run something like these first, oh dear, git is complicated!!

git remote rm origin
rm -rf .git/refs/original/ .git/refs/remotes/ .git/*_HEAD .git/logs/
git for-each-ref --format="%(refname)" refs/original/ | xargs -n1 --no-run-if-empty git update-ref -d

You might also need to remove some tags, thanks Zitrax:

git tag | xargs git tag -d

I put all this in a script: git-gc-all-ferocious.

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Solution 2:

As described here, simply use

git reflog expire --expire-unreachable=now --all
git gc --prune=now

git reflog expire --expire-unreachable=now --all removes all references of unreachable commits in reflog.

git gc --prune=now removes the commits themselves.

Attention: Only using git gc --prune=now will not work since those commits are still referenced in the reflog. Therefore, clearing the reflog is mandatory.

Solution 3:

As mentioned in this SO answer, git gc can actually increase the size of the repo!

See also this thread

Now git has a safety mechanism to not delete unreferenced objects right away when running ‘git gc‘.
By default unreferenced objects are kept around for a period of 2 weeks. This is to make it easy for you to recover accidentally deleted branches or commits, or to avoid a race where a just-created object in the process of being but not yet referenced could be deleted by a ‘git gc‘ process running in parallel.

So to give that grace period to packed but unreferenced objects, the repack process pushes those unreferenced objects out of the pack into their loose form so they can be aged and eventually pruned.
Objects becoming unreferenced are usually not that many though. Having 404855 unreferenced objects is quite a lot, and being sent those objects in the first place via a clone is stupid and a complete waste of network bandwidth.

Anyway… To solve your problem, you simply need to run ‘git gc‘ with the --prune=now argument to disable that grace period and get rid of those unreferenced objects right away (safe only if no other git activities are taking place at the same time which should be easy to ensure on a workstation).

And BTW, using ‘git gc --aggressive‘ with a later git version (or ‘git repack -a -f -d --window=250 --depth=250‘)

The same thread mentions:

 git config pack.deltaCacheSize 1

That limits the delta cache size to one byte (effectively disabling it) instead of the default of 0 which means unlimited. With that I’m able to repack that repository using the above git repack command on an x86-64 system with 4GB of RAM and using 4 threads (this is a quad core). Resident memory usage grows to nearly 3.3GB though.

If your machine is SMP and you don’t have sufficient RAM then you can reduce the number of threads to only one:

git config pack.threads 1

Additionally, you can further limit memory usage with the --window-memory argument to ‘git repack‘.
For example, using --window-memory=128M should keep a reasonable upper bound on the delta
search memory usage although this can result in less optimal delta match if the repo
contains lots of large files.


On the filter-branch front, you can consider (with cautious) this script

#!/bin/bash
set -o errexit

# Author: David Underhill
# Script to permanently delete files/folders from your git repository.  To use 
# it, cd to your repository's root and then run the script with a list of paths
# you want to delete, e.g., git-delete-history path1 path2

if [ $# -eq 0 ]; then
    exit 0
fi

# make sure we're at the root of git repo
if [ ! -d .git ]; then
    echo "Error: must run this script from the root of a git repository"
    exit 1
fi

# remove all paths passed as arguments from the history of the repo
files=$@
git filter-branch --index-filter "git rm -rf --cached --ignore-unmatch $files" HEAD

# remove the temporary history git-filter-branch otherwise leaves behind for a long time
rm -rf .git/refs/original/ && git reflog expire --all &&  git gc --aggressive --prune

Solution 4:

git gc --prune=now, or low level git prune --expire now.

Solution 5:

Each time your HEAD moves, git tracks this in the reflog. If you removed commits, you still have “dangling commits” because they are still referenced by the reflog for ~30 days. This is the safety-net when you delete commits by accident.

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You can use the git reflog command remove specific commits, repack, etc.., or just the high level command:

git gc --prune=now

Solution 6:

You can use git forget-blob.

The usage is pretty simple git forget-blob file-to-forget. You can get more info here

https://ownyourbits.com/2017/01/18/completely-remove-a-file-from-a-git-repository-with-git-forget-blob/

It will disappear from all the commits in your history, reflog, tags and so on

I run into the same problem every now and then, and everytime I have to come back to this post and others, that’s why I automated the process.

Credits to contributors such as Sam Watkins

References