Prep for publication

GitDeepDive.org

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+#+OPTIONS: ^:{} toc:nil author:nil num:nil
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 * Git Deep Dive
   A Version 1 Technical Meetup talk covering the deep internals of git.
 
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       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) 
+   2) Run the script =largeFile-setup.sh=. This will create another
+      git repository in =largeFileRepo= and populate it with the same
+      commits as in =simpleRepo=, and then puts in some more to create
+      and manipulate a large binary file, and then to remove it. This
+      will be used for the demonstration to remove a file completely
+      from the repository.
+   3) Run the script =gitDemo.sh=. This will replicate a previous git
+      repository as a bare repo in
+ =devTeamDemo/javaBootcampNoEclipse.git=, and then create a
+      number of clones to represent the actions of a team lead and two
+      developers, and mimic collaborative development among
+      them. =gitDemo.sh= takes one optional parameter, =-s=, which
+      will cause the progression to stop for 15 seconds following each
+      "actor's" push in order to afford the opportunity to look at the
+      git log.
+   4) Use the =gpg= utility to generate a key-pair so that you can
+      work through the commit- and tag-signing slide and sample
+      commands. If you have access to =gpg2= and not =gpg=, you'll
+      need to set the following =git config= to make sure it's picked
+      up: =git config --global gpg.program gpg2=.
+   5) Open the file =GitDeepDive.pdf=, and as you go through the
+      slides, refer to the /Sample Commands/ section below for
+      commands you can execute to get further insights.
+
+** Sample commands
+
+*** Slide: Configuration
+    #+BEGIN_SRC shell
+      # Go to where the GitDeepDive.pdf file is and set your BASE_DIR
+      # environment variable.
+      cd <where-you-have-this-repo-cloned-to>
+      export BASE_DIR=$(pwd)
+      # List your basic git config
+      git config --list
+      # Go into the simple repo location and look at the various config
+      # contexts
+      cd ${BASE_DIR}/simpleRepo
+      git config --local --list
+      git config --global --list
+      git config --system --list
+      # Set some settings
+      git config --global user.name "<YourName>"
+      git config --global user.email "<YourEmailAddress>"
+      # Use a text editor to edit your config
+      git config -e
+    #+END_SRC
+
+*** Slide: fetch and merge, not pull
+    #+BEGIN_SRC shell
+      # Go into the clone belonging to one of the developers in the
+      # development team demo area
+      cd ${BASE_DIR}/devTeamDemo/javaBootcampNoEclipse.dev1
+      # Update the clone, but don't merge anything
+      git fetch --prune
+      # Review the local and remote branches.
+      git branch -va
+    #+END_SRC
+
+*** Slide: Merging approaches: fast-forward
+    #+BEGIN_SRC shell
+      cd ${BASE_DIR}/simpleRepo
+      # Check out the master branch and review it's log
+      git checkout master
+      git log --decorate --graph --oneline --all
+      # Merge in the Rel1 branch and review the new log.
+      git merge Rel1
+      git log --decorate --graph --oneline --all
+    #+END_SRC
+
+*** Slide: Merging approaches: merging strategies
+    #+BEGIN_SRC shell
+      cd ${BASE_DIR}/simpleRepo
+      # Check out the master branch, merge the Rel2 branch and review the
+      # new log.
+      git checkout master
+      # You'll be prompted for a commit message here.
+      git merge Rel2
+      git log --decorate --graph --oneline --all
+    #+END_SRC
+
+*** Slide: Merging approaches: Rebase
+    #+BEGIN_SRC shell
+      # Remove and refresh the simpleRepo
+      ${BASE_DIR}/merge-setup.sh
+      cd ${BASE_DIR}/simpleRepo
+
+      # Check out master, review its log, merge Rel1 and review the log
+      git checkout master
+      git log --decorate --graph --oneline --all
+      git merge Rel1
+      git log --decorate --graph --oneline --all
+
+      # Check out Rel2
+      git checkout Rel2
+      # Rebase Rel2 onto the now-new master
+      git rebase master
+      # Review the log
+      git log --decorate --graph --oneline --all
+    #+END_SRC
+
+*** Slide: refs
+    #+BEGIN_SRC shell
+      # Remove and refresh the simpleRepo
+      ${BASE_DIR}/merge-setup.sh
+      cd ${BASE_DIR}/simpleRepo
+
+      # Look at the contents of .git/refs/heads and one of the heads itself
+      ls -l .git/refs/heads/
+      cat .git/refs/heads/Rel2
+
+      # Tag a branch, look at the branch ref and the tag ref
+      git tag Rel1.0 Rel1
+      cat .git/refs/heads/Rel1
+      cat .git/refs/tags/Rel1.0
+
+      # Look at the HEAD ref
+      cat .git/HEAD
+
+      # Go to another clone and look at the refs for the origin remote
+      cd ${BASE_DIR}/devTeamDemo/javaBootcampNoEclipse.dev1
+      ls -l .git/refs/remotes/origin/
+      # .git/packed-refs contains the refs that haven't been interacted with
+      # yet.
+      cat .git/packed-refs
+    #+END_SRC
+
+*** Slide: Annotated tags
+    #+BEGIN_SRC shell
+      cd ${BASE_DIR}/simpleRepo
+
+      # Look at a "lightweight" tag
+      cat .git/refs/tags/Rel1.0
+      # What type of object is it pointing to?
+      git cat-file -t $(cat .git/refs/tags/Rel1.0)
+      # What's in the object it's pointing to
+      git cat-file -p $(cat .git/refs/tags/Rel1.0)
+
+      # Create an annotated tag and look at *it*
+      git tag -a -m "Formal release of 1.0" Rel1.0.prod Rel1
+      cat .git/refs/tags/Rel1.0.prod
+      # What type of object is it pointing to?
+      git cat-file -t $(cat .git/refs/tags/Rel1.0.prod)
+      # What's in the object it's pointing to
+      git cat-file -p $(cat .git/refs/tags/Rel1.0.prod)
+    #+END_SRC
+
+*** Slide: blame
+    #+BEGIN_SRC shell
+      # Look at the lines of the file on master
+      git checkout master
+      git blame information.md
+      # .. and on Rel1
+      git checkout Rel1
+      git blame information.md
+      # And on master after Rel2 has been merged in.
+      git merge Rel2
+      git blame information.md
+      # Slide
+    #+END_SRC
+
+*** Slide: Tag and commit signing
+    #+BEGIN_SRC shell
+      # Look at your secret keys
+      gpg --list-secret-keys
+
+      # Check out master and make a change to information.md
+      git checkout master
+      cat <<EOF >> information.md
+      An additional line for demonstrating commit-signing.
+
+      EOF
+
+      # Add and commit the change, signing the commit.
+      git add information.md
+      git commit -S<secretKeyID> -m "Update to information.md"
+
+      # Look at the commit object
+      git cat-file -p master
+
+      # Create an annotated tag from the Rel2 branch, signing it.
+      git tag -s -u <secretKeyID> -m "Release 2." Rel2.0 Rel2
+      # Look at the tag object
+      git cat-file -p Rel2.0
+
+      # Verify the signed tag and the signed commit.
+      git tag -v Rel2.0
+      git log --show-signature -1
+    #+END_SRC
+
+*** Slide: Git Objects -- blobs
+    #+BEGIN_SRC shell
+      # Generate the SHA1 of the contents of the ~/.bash_history file as
+      # though git would
+      cat ~/.bash_history | git hash-object --stdin
+    #+END_SRC
+
+*** Slide: Git Objects -- trees
+    #+BEGIN_SRC shell
+      cd ${BASE_DIR}/devTeamDemo/javaBootcampNoEclipse.dev1
+      # Get the tree object for the latest version of the top-level of the
+      # project
+      git cat-file -p master | grep '^tree'
+      # Look at the contents of that tree object:
+      git cat-file -p $(git cat-file -p master | grep '^tree' | sed 's/^tree //')
+    #+END_SRC
+
+*** Slide: Git Objects -- commits
+    #+BEGIN_SRC shell
+      cd ${BASE_DIR}/simpleRepo
+      git log --graph --all --decorate --oneline
+      git cat-file -p HEAD
+      git cat-file -p <anyOtherCommitId>
+    #+END_SRC
+
+*** Slide: Git Objects -- tags
+    #+BEGIN_SRC shell
+      # Find all the tag objects
+      git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize)' --batch-all-objects | grep tag
+      git cat-file -p <anyOfTheTagObjects>
+    #+END_SRC
+
+*** Slide: "Content Addressable Filesystem"
+    #+BEGIN_SRC shell
+      # Find all the objects, and select one that refers to a file
+      git rev-list --all --objects
+      # Look at the contents of the selected object
+      git cat-file -p <selectedBlobObject>
+      # Use git to get the SHA1 of the contents of that object
+      git cat-file -p <selectedBlobObject> | git hash-object --stdin
+      # The name of the file for that object is based on the SHA1.
+      ls -l .git/objects/...
+    #+END_SRC
+
+*** Slide: The reflog
+    #+BEGIN_SRC shell
+      # Look at the reflog, then clear it completely and look at it again.
+      git reflog
+      git reflog expire --expire=now --expire-unreachable=now --verbose --all
+      git reflog
+    #+END_SRC
+
+*** Slide: fsck and gc
+    #+BEGIN_SRC shell
+      git fsck
+      git gc
+    #+END_SRC
+
+*** Slide: Useful commands
+    #+BEGIN_SRC shell
+      # Go into the repo where the large file had been created
+      cd ${BASE_DIR}/largeFileRepo
+      # List all the objects in increasing order of object size.
+      git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize)' --batch-all-objects | sed -n 's/^blob //p' | sort -n --key=2
+      # Look for the file name associated with an object
+      git rev-list --objects --all | grep <blobID>
+      # Look for the commits that made changes to a specific file
+      git log --follow -- "largeInformation.md"
+    #+END_SRC
+
+*** Slide: Permanently removing a file from your git db [1/2]
+    #+BEGIN_SRC shell
+
+      # Preserve information on the tags, as you may need this later.
+      for tag in $(git tag)
+      do
+        echo "${tag},$(git log --format="%H,\"%cn\",\"%ci\",\"%s\"" ${tag} | head -1)"
+      done | tee /tmp/tag_list.csv
+
+      # Create a local branch for all the remote branches. This does nothing
+      # in this demo as there is no remote.
+      for branch in $(git branch -r | grep -v HEAD | sed 's/\ \ origin\///')
+      do
+        git branch ${branch} origin/${branch}
+      done
+
+      # Check out each branch and determine the amount of space it uses
+      for branch in $(git branch | sed 's/^..//')
+      do
+        git checkout -q ${branch}
+        du -sk . | sed "s/\./${branch}/"
+      done | tee /tmp/branch_sizes.out
+
+      # Check out the Rel1 branch
+      git checkout Rel1
+      # Use git-filter-branch to remove the file from all the commits on the
+      # branch
+      git filter-branch --tree-filter 'rm -f largeInformation.md' --prune-empty HEAD
+      # Update refs (will fail for some branches)
+      git for-each-ref --format="%(refname)" refs/original/ | xargs -n 1 git update-ref -d
+
+      # Do the same for all the other branches
+      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 /tmp/cleanup.out
+
+      # Clear out the reflog
+      git reflog expire --expire-unreachable=now --all
+      # Run the garbage collector on the repository
+      git gc --prune=now
+      # Run an FSCK on the repo
+      git fsck --unreachable --no-reflogs
+
+      # Check out each branch again and determine the amount of space it
+      # uses
+      for branch in $(git branch | sed 's/^..//')
+      do
+        git checkout -q ${branch}
+        du -sk . | sed "s/\./${branch}/"
+      done | tee /tmp/branch_sizes_post_process.out
+    #+END_SRC