Rewrite Github History

[yvovandoorn]

• Removes large PNG files
• removes large PDF files

Rewriting history is usually left to politicians. In this case its good to trim down the repo history for those getting started to get a reduced, in download size, repo.

@bridgetkromhout was interested in owning once the dust had settled.

[yvovandoorn]

So I wanted to learn how to do this and ran it as an experiment on a forked version of devopsdays-web. I'm sure there are more practical ways, but it was a good exercise none the less.

References of inspiration:

Step 1 was installing bfg:
brew install bfg

I started by cloning out a regular version of the repo (my fork):
git clone git@github.com:yvovandoorn/devopsdays-web.git

Then I needed to get all shas ever and a list of big objects:
git rev-list --objects --all | sort -k 2 > allfileshas.txt

git gc && git verify-pack -v .git/objects/pack/pack-*.idx | egrep "^\w+ blob\W+[0-9]+ [0-9]+ [0-9]+$" | sort -k 3 -n -r > bigobjects.txt

So I have a list of all the files and a list of bigobjects. Time to match 'em up:

for SHA in cut -f 1 -d\ < bigobjects.txt; do echo $(grep $SHA bigobjects.txt) $(grep $SHA allfileshas.txt) | awk '{print $1,$3,$7}' >> bigtosmall.txt; done

My mission was just to target PDFs and PNGs:
egrep "png|pdf" bigtosmall.txt > allpdf_and_png_files.txt

So now I have a list of PDFs and PNGs, but some are still real (like a lot of logo.pngs). This is where I got a little creative in capturing the negative output.

for i in $(awk '{ print $3 }' allpdf_and_png_files.txt ); do file $i; done | grep "No such file" > removed_files.txt

Then run it through awk, sort and uniq to make sure to weed out any potential duplicates (sometimes the sha + blog matching results into duplicates).

awk -F":" '{ print $1 }' removed_files.txt | sort | uniq > removed_files_list.txt

This got me a list of files that were truly out of HEAD and shouldn't be part of the history anymore. Having used git filter-branch in the past, I knew it was a PITA for it to do it as it takes forever. I remembered BFG but BFG is path-independent (ref: http://stackoverflow.com/questions/21142986/remove-filenames-from-specific-path). I needed assurance that I was removing files that needed to be removed. BFG does have --strip-blobs-with-ids <blob-ids-file> as an option. So now I needed to get all the blob IDs on the files I wanted to remove.

for file in $(cat removed_files_list.txt); do git log --format=%H -- $file | xargs -IcommitId git rev-parse commitId:$file; done > blobs.txt

This produced some fatals only because of some of the files we're trying to remove were no longer there in subsequent commits. So not a bad thing. The file produced all blobs needed to be removed. I cleaned it out (some entries had initial commit of said file to be "blob ID only".

awk -F":" '{ print $1 }' blobs.txt > blobs-with-ids

Now I had the blobs!

BFG only works on mirrored versions of a checkout so off I went to checkout my repo again:

git clone --mirror git@github.com:yvovandoorn/devopsdays-web.git devopsdays-web-mirror

I copied my blobs-with-ids file to ~/Development (directory that hosts all my git repos) and ran:
bfg -bi blobs-with-ids devopsdays-web-mirror

Which produced a result indicating all deleted files.

I changed into the mirrored directory and ran (according to BFG instructions):
git reflog expire --expire=now --all && git gc --prune=now --aggressive

Now for a final git push to my fork.

I did a mkdir size-diff && cd size-diff && git clone git@github.com:yvovandoorn/devopsdays-web.git devopsdays-web-cleaned && git clone git@github.com:devopsdays/devopsdays-web.git

Then ran du -sh *(/), which produced:

Development/size-diff » du -sh *(/)
321M    devopsdays-web
247M    devopsdays-web-cleaned

Result: 74MB trimmed!

Sources of inspiration

• http://naleid.com/blog/2012/01/17/finding-and-purging-big-files-from-git-history
• https://rtyley.github.io/bfg-repo-cleaner/

[mattstratton]

Very cool and this is a useful write up!

[bridgetkromhout]

Very cool. Go ahead and do it for real and write a blog post from these notes!

[yvovandoorn]

And done!

323M    devopsdays-web
246M    devopsdays-web-new

[bridgetkromhout]

Gah. I had a branch I created off of mattstratton/redesign, and didn't check to make sure it was up to date. When I pushed it up, it brought all the giant files back.

Falling asleep here soon. Will try to reverse in the morning. (I deleted the branch - bridget-program-updates - but the files it brought in are still in history. I suspect this is going to happen to more people than just me.)

[yvovandoorn]

Ok re-did this again with filter.

Generating SHAs & objects
git rev-list --objects --all | sort -k 2 > allfileshas.txt
git gc && git verify-pack -v .git/objects/pack/pack-*.idx | egrep "^\w+ blob\W+[0-9]+ [0-9]+ [0-9]+$" | sort -k 3 -n -r > bigobjects.txt

Combining SHAs & objects to names and then sizing then big to small
for SHA in cut -f 1 -d\ < bigobjects.txt; do echo $(grep $SHA bigobjects.txt) $(grep $SHA allfileshas.txt) | awk '{print $1,$3,$7}' >> bigtosmall.txt; done

Filtering out just PDFs and PNGs
egrep "png|pdf" bigtosmall.txt > allpdf_and_png_files.txt

Grabbing no longer existing PDFs and PNGs
for i in $(awk '{ print $3 }' allpdf_and_png_files.txt ); do file $i; done | grep "No such file" > removed_files.txt

Get rid of all the other things, I just care about files.
awk -F":" '{ print $1 }' removed_files.txt | sort | uniq > removed_files_list.txt

sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/ /g' removed_files_list.txt

Then I got lazy and just posted all the files at once (yes I could've just done a cat removed_files_list_lines but meh).
git filter-branch -f --index-filter "git rm -rf --cached --ignore-unmatch static/events/2016-amsterdam/devopsdays_2016_-_sponsor_prospectus.pdf static/events/2016-amsterdam/speakers/adam-jacob.png static/events/2016-amsterdam/speakers/andrew-farley.png static/events/2016-amsterdam/speakers/avishai-ish-shalom.png static/events/2016-amsterdam/speakers/bernd-erk.png static/events/2016-amsterdam/speakers/christoph-andreas-torlinsky.png static/events/2016-amsterdam/speakers/daniel-van-gils.png static/events/2016-amsterdam/speakers/desmond-delissen.png static/events/2016-amsterdam/speakers/erica-baker.png static/events/2016-amsterdam/speakers/gopal-ramachandran.png static/events/2016-amsterdam/speakers/hannah-foxwell.png static/events/2016-amsterdam/speakers/jason-yee.png static/events/2016-amsterdam/speakers/jody-wolfborn.png static/events/2016-amsterdam/speakers/ken-mugrage.png static/events/2016-amsterdam/speakers/marco-ceppi.png static/events/2016-amsterdam/speakers/melanie-rieback.png static/events/2016-amsterdam/speakers/michael-friedrich.png static/events/2016-amsterdam/speakers/pavel-chunyayev.png static/events/2016-amsterdam/speakers/robert-den-broeder.png static/events/2016-amsterdam/speakers/simon-fisher.png static/events/2016-amsterdam/speakers/stefan-stolzle.png static/events/2016-amsterdam/speakers/takahiko-ito.png static/events/2016-amsterdam/speakers/victoria-jeffrey.png static/events/2016-amsterdam/speakers/warner-moore.png static/events/2016-amsterdam/speakers/will-button.png static/events/2016-london/presenters/images/Philippe-Guenet.png static/events/2016-london/speakers/andi-mann.png static/events/2016-london/speakers/benjamin-wootton.png static/events/2016-london/speakers/casey-west.png static/events/2016-london/speakers/claire-agutter.png static/events/2016-london/speakers/gareth-rushgrove.png static/events/2016-london/speakers/gene-kim.png static/events/2016-london/speakers/jeromy-carriere.png static/events/2016-london/speakers/joanne-molesky.png static/events/2016-london/speakers/john-clapham.png static/events/2016-london/speakers/justin-cormack.png static/events/2016-london/speakers/kris-saxton.png static/events/2016-london/speakers/oliver-wood.png static/events/2016-london/speakers/thiago-almeida.png static/events/2016-minneapolis/speakers/allan-espinosa.png static/events/2016-minneapolis/speakers/ben-zvan.png static/events/2016-minneapolis/speakers/charity-majors.png static/events/2016-minneapolis/speakers/jeff-smith.png static/events/2016-minneapolis/speakers/megan-carney.png static/events/2016-minneapolis/speakers/nicole-forsgren.png static/events/2016-minneapolis/speakers/sarah-goff-dupont.png static/img/events/2016-atlanta/logo.png static/img/events/2016-chicago/logo.png static/img/events/2016-minneapolis/logo.png static/img/sponsors/2016-chef.png static/img/sponsors/2016-thoughtworks.png static/img/sponsors/thoughtworks.png themes/devopsdays-responsive/static/images/devopsdays-brain.png" -- --all

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

And off it goes
git push --all --force