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Éibhear Ó hAnluain 2018-06-26 09:03:58 +01:00
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simpleRepo
largeFileRepo
devTeamDemo

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* Git Deep Dive
A Version 1 Technical Meetup talk covering the deep internals of git.
** Introduction
This is the slide-deck and set-up scripts used to give the /Git
Deep Dive/ technical meet-up talk on [2018-06-25 Mon] in Version 1,
by Éibhear Ó hAnluain.
The pack comes with the following:
- This document
- The slide-deck, =GitDeepDive.pdf=
- A script to set up a simple git repository for exploration
purposes: =merge-setup.sh=
- A script to set up the mimic of a development team and processes:
=gitDemo.sh=
- A script to set up another simple repository to run through the
process for completely clearing a file out of a git database:
=largeFile-setup.sh=.
- A =.gitignore= file.
** Setup
1) Run the script =merge-setup.sh=. This will create a git
repository in =simpleRepo= and populate it with some
commits. The commits in this repository will correspond to the
diagrams in the slide-deck that relate to merging.
2)

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Setup
bash ~/eibhear_org/scripts/gitDemo.sh
bash ~/eibhear_org/Version1/TechTalks/merge-setup.sh
gpg2 --generate-key
git config --global gpg.program gpg2
Slide: Configuration
git config --list
cd ~/tmp/DeepDive1
git config --local --list
git config --global --list
git config --system --list
git config --global user.name "Éibhear Ó hAnluain"
git config --global user.email "eibhear.ohanluain@version1.com"
git config -e
# Slide
Slide: fetch and merge, not pull
cd ~/tmp/gitDemo/javaBootcampNoEclipse.dev1
git fetch --prune
# Slide
git branch -va
# Slide
Slide: Merging approaches: fast-forward
cd ~/tmp/DeepDive1
git checkout master
git log --decorate --graph --oneline --all
git merge Rel1
# Slide
git log --decorate --graph --oneline --all
# Slide
Slide: Merging approaches: merging strategies
cd ~/tmp/DeepDive1
git checkout master
git merge Rel2
git log --decorate --graph --oneline --all
# Slide
Slide: Merging approaches: Rebase
bash ~/eibhear_org/Version1/TechTalks/merge-setup.sh
cd ~/tmp/DeepDive1
git checkout master
git log --decorate --graph --oneline --all
git merge Rel1
git log --decorate --graph --oneline --all
git checkout Rel2
git rebase master
# Slide
git log --decorate --graph --oneline --all
# Slide
Slide: refs
bash ~/eibhear_org/Version1/TechTalks/merge-setup.sh
cd ~/tmp/DeepDive1
ls -l .git/refs/heads/
cat .git/refs/heads/Rel2
# Slide
git tag Rel1.0 Rel1
cat .git/refs/heads/Rel1
cat .git/refs/tags/Rel1.0
cat .git/HEAD
# Slide
cd ~/tmp/gitDemo/javaBootcampNoEclipse.dev1
ls -l .git/refs/remotes/origin/
cat .git/packed-refs
# Slide
Slide: Annotated tags
cd ~/tmp/DeepDive1
cat .git/refs/tags/Rel1.0
git cat-file -t $(cat .git/refs/tags/Rel1.0)
git cat-file -p $(cat .git/refs/tags/Rel1.0)
# Slide
git tag -a -m "Formal release of 1.0" Rel1.0.prod Rel1
cat .git/refs/tags/Rel1.0.prod
git cat-file -t $(cat .git/refs/tags/Rel1.0.prod)
git cat-file -p $(cat .git/refs/tags/Rel1.0.prod)
# Slide
Slide: blame
git blame information.md
git checkout Rel1
git blame information.md
git merge Rel2
git blame information.md
# Slide
Slide: Tag and commit signing
gpg --list-secret-keys
git checkout master
# Edit information.md
git commit -a -Seibhear.ohanluain@version1.com -m "Update to information.md"
git cat-file -p master
git tag -s -u eibhear.ohanluain@version1.com -m "Release 2." Rel2.0 Rel2
git cat-file -p Rel2.0
# Slide
git tag -v Rel2.0
git log --show-signature -1
# Slide
Slide: Git Objects -- blobs
cat ~/.bash_history | git hash-object --stdin
# Slide
Slide: Git Objects -- trees
cd ~/tmp/gitDemo/javaBootcampNoEclipse.dev1
cat .git/refs/heads/master
git cat-file -p <treeObject>
# Slide
Slide: Git Objects -- commits
cd ~/tmp/DeepDive1
git log --graph --all --decorate --oneline
git cat-file -p HEAD
git cat-file -p <objectId>
# Slide
Slide: Git Objects -- tags
git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize)' --batch-all-objects | grep tag
git cat-file -p <tagObject>
# Slide
Slide: "Content Addressable Filesystem"
git rev-list --all --objects
git cat-file -p <blobObject>
git cat-file -p <blobObject> | git hash-object --stdin
ls -l .git/objects/...
# Slide
Slide: The reflog
git reflog
git reflog expire --expire=now --expire-unreachable=now --verbose --all
git reflog
# Slide
Slide: fsck and gc
git fsck
git gc
# Slide
Slide: Useful commands
bash ~/eibhear_org/Version1/TechTalks/largeFile-setup.sh
cd ~/tmp/DeepDive1
git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize)' --batch-all-objects | sed -n 's/^blob //p' | sort -n --key=2
git rev-list --objects --all | grep <blobID>
git log --follow -- "largeInformation.md"
# Slide
Slide: Permanently removing a file from your git db [1/2]
for tag in $(git tag)
do
echo "${tag},$(git log --format="%H,\"%cn\",\"%ci\",\"%s\"" ${tag} | head -1)"
done | tee ../tag_list.csv
for branch in $(git branch -r | grep -v HEAD | sed 's/\ \ origin\///')
do
git checkout ${branch}
done
for branch in $(git branch | sed 's/^..//')
do
git checkout -q ${branch}
du -sk . | sed "s/\./${branch}/"
done | tee ../branch_sizes.out
# Slide
git checkout Rel1
# Slide
git filter-branch --tree-filter 'rm -f largeInformation.md' --prune-empty HEAD
# Slide
git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d
# Slide
for branch in Rel2 Rel3 Rel4 master
do
git checkout ${branch}
git filter-branch --tree-filter 'rm -f largeInformation.md' --prune-empty HEAD
git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d
done | tee ../cleanup.out
# Slide
git reflog expire --expire-unreachable=now --all
# Slide
git gc --prune=now
# Slide
git fsck --unreachable --no-reflogs
# Slide
for branch in $(git branch | sed 's/^..//')
do
git checkout -q ${branch}
du -sk . | sed "s/\./${branch}/"
done | tee ../branch_sizes_post_process.out
# Slide
# End

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#!/bin/bash
# Run the merge set-up script to create a clean DeepDive1 dir.
SCRIPT_DIR=$(cd $(dirname ${0}); pwd)
declaim () {
echo
echo ${*}
echo "==============="
echo
}
REPO_DIR=${SCRIPT_DIR}/largeFileRepo
${SCRIPT_DIR}/merge-setup.sh ${REPO_DIR}
cd ${REPO_DIR}
declaim "Creating tags"
git tag Rel1.0.lw Rel1
git tag -m "An annotated tag for the Rel1 release" Rel1.0.a Rel1
git tag Rel2.0.lw Rel2
git tag -m "An annotated tag for the Rel1 release" Rel2.0.a Rel2
declaim "Merging Rel1 and Rel2 into master"
git checkout master
git merge Rel1
git merge -m "commit8" Rel2
declaim "Repository size in kibibytes: $(du -sk .)"
declaim "Creating a 10MiB binary file"
gzip -9 -c information.md > information_compressed.out
counter=0
while [ ${counter} -lt 15 ];
do
cat information_compressed.out information_compressed.out > information_compressed2.out
mv information_compressed2.out information_compressed.out
counter=$(( $counter + 1 ))
done
mv information_compressed.out largeInformation.md
declaim "Adding and commiting that new file"
git add largeInformation.md
git commit -m "A large, awkwardly binary file"
declaim "Creating and checking out the Rel3 branch"
git checkout -b Rel3
declaim "Modifying the large binary file on Rel3"
cat information.md information.md information.md >> largeInformation.md
declaim "Adding and commiting that change to the binary file."
git add largeInformation.md
git commit -m "Changes to that large file"
declaim "Creating and checking out the Rel4 branch"
git checkout master
git checkout -b Rel4
declaim "Modifying the large binary file on Rel4"
cat largeInformation.md largeInformation.md > largeInformation2.md
rm largeInformation.md
mv largeInformation{2,}.md
declaim "Adding and commiting that change to the binary file."
git add largeInformation.md
git commit -m "An even larger file"
declaim "Merging Rel3 and Rel4 into master"
git checkout master
git merge Rel3
git merge -s recursive -Xtheirs -m "Merge of Rel4 into master" Rel4
declaim "Removing that large file, now."
git rm largeInformation.md
git commit -m "large binary file gone again"
git log --oneline --graph --decorate --all
declaim "Repository size in kibibytes: $(du -sk .)"

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#!/bin/bash
declaim () {
echo
echo ${*}
echo "==============="
echo
}
SCRIPT_DIR=$(cd $(dirname ${0}); pwd)
REPO_DIR=${SCRIPT_DIR}/simpleRepo
if [ ${#} -eq 1 ]; then
REPO_DIR=${1}
elif [ ${#} -gt 1 ]; then
exit
fi
declaim "Creating empty repository: ${REPO_DIR}"
rm -rf ${REPO_DIR}
mkdir -vp ${REPO_DIR}
cd ${REPO_DIR}
declaim "Initialising it as a git repository"
git init .
git config --local user.name "Gaius Julius Caesar"
git config --local user.email "gjcaesar@pontifexmaximus.rm"
declaim "Creating a text file"
cat <<EOF > information.md
# Test file
This is a file for demonstration purposes
EOF
declaim "Adding and commiting that text file. The first commit"
git add information.md
git commit -m "commit1"
declaim "Updating the text file"
echo "This is a second line of information." >> information.md
echo >> information.md
declaim "Adding and commiting that text file. The second commit"
git add information.md
git commit -m "commit2"
declaim "Updating the text file for the second time"
echo "This is a third line of information." >> information.md
echo >> information.md
declaim "Adding and commiting that text file. The third commit"
git add information.md
git commit -m "commit3"
declaim "Creating and checking out the Rel1 branch"
git checkout -b Rel1
declaim "Updating the text file on the Rel1 branch"
cat <<EOF >> information.md
# Rel1 information
This is more information added as part of Rel1
EOF
declaim "Adding and commiting that text file. The fourth commit"
git add information.md
git commit -m "commit4"
declaim "Updating the text file on the Rel1 branch again"
mv -v information.md{,.hold}
cat information.md.hold | sed 's/of Rel1$/of Rel1./' > information.md
rm information.md.hold
declaim "Adding and commiting that text file. The fifth commit"
git add information.md
git commit -m "commit5"
declaim "Creating and checking out the Rel2 branch"
git checkout master
git checkout -b Rel2
declaim "Updating the text file on the Rel2 branch"
mv information.md{,.hold}
cat <<EOF > information.md
# Rel2 information
This is more information added as part of Rel2
EOF
cat information.md.hold >> information.md
rm information.md.hold
declaim "Adding and commiting that text file. The sixth commit"
git add information.md
git commit -m "commit6"
declaim "Updating the text file on the Rel2 branch again"
mv information.md{,.hold}
cat information.md.hold | sed 's/of Rel2$/of Rel2./' > information.md
rm information.md.hold
declaim "Adding and commiting that text file. The seventh commit"
git add information.md
git commit -m "commit7"
declaim "Checking out master"
git checkout master
git log --oneline --graph --decorate --all