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Éibhear Ó hAnluain 2022-09-23 20:33:41 +01:00
parent 5022169c08
commit d8288cef57
Signed by: eibhear
GPG key ID: D124FE9CF2177106
2 changed files with 246 additions and 283 deletions
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@ -86,8 +86,9 @@
- Submarining :: the structure of a commit, "Content Addressable Filesystem", git objects
- Unmanned submersibles :: the reflog, =fsck= and =gc=, finding and dealing with specific git objects
** About Éibhear Ó hAnluain
- Solutions Architect
+ eibhear.geo@gmail.com
- Enterprise and Solutions Architect
+ e-mail: [[mailto:eibhear.geo@gmail.com][eibhear.geo@gmail.com]]
+ [matrix]: [[https://matrix.to/#/@eibhear:matrix.gibiris.org][@eibhear:matrix.gibiris.org]], [[https://matrix.to/#/@eibhear:matrix.org][@eibhear:matrix.org]]
- Software engineer since 1994
- Using revision control since 1994: _subversion_, _git_,
_IBM/Rational/Atria ClearCase_, _RCS_, _VSS_, _CVS_, _Serena
@ -107,7 +108,8 @@
git config --local --list
git config --global --list
git config --system --list
git config [--system|--global|--local] <key> <value>
git config [--system|--global|--local] <key> \
<value>
git config -e
#+END_SRC
** =fetch= and =merge=, not =pull=
@ -196,315 +198,275 @@
#+REVEAL_HTML: </div>
#+REVEAL_HTML: </div>
** Merging appraoches: Decision tree
** Merging approaches: Decision tree
file:./images/merge-decision-tree-chart.png
* The Shallows
**
*** A little deeper :B_block:BMCOL:
:PROPERTIES:
:BEAMER_col: 0.9
:BEAMER_env: block
:END:
file:./images/Naufragio_por_Gustavo_Gerdel.jpg
Let's go a little deeper
#+latex: {\tiny
By Ggerdel - Foto de: Gustavo Gerdel (BAB Buceo) [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons
#+latex: }
** Refs
*** Refs
- Branches
#+BEGIN_SRC
$ ls -1 .git/refs/heads/*
.git/refs/heads/gitlab_10.x_upgrade
.git/refs/heads/gitlab-ce-8.17
.git/refs/heads/gitlab-ce-9.1.4-defectFix
.git/refs/heads/master
#+CAPTION: By Ggerdel - Foto de: Gustavo Gerdel (BAB Buceo) [[https://creativecommons.org/licenses/by-sa/4.0][CC BY-SA 4.0]], via Wikimedia Commons
#+ATTR_HTML: :width 70%
file:./images/Naufragio_por_Gustavo_Gerdel.jpg
** Refs -- branches
#+BEGIN_SRC shell
$ ls -1 .git/refs/heads/*
.git/refs/heads/gitlab_10.x_upgrade
.git/refs/heads/gitlab-ce-8.17
.git/refs/heads/gitlab-ce-9.1.4-defectFix
.git/refs/heads/master
$ cat .git/refs/heads/gitlab-ce-8.17
c63767d0b9b520f36a533237624dfaa1256b463c
#+END_SRC
** Refs
*** Refs
- tags
#+BEGIN_SRC
$ ls -1 .git/refs/tags/
gitlab-cookbook-for-10.7.3
gitlab-cookbook-initial
gitlab-cookbook-rebaseline
$ cat .git/refs/heads/gitlab-ce-8.17
c63767d0b9b520f36a533237624dfaa1256b463c
#+END_SRC
** Refs -- tags
- tags
#+BEGIN_SRC shell
$ ls -1 .git/refs/tags/
gitlab-cookbook-for-10.7.3
gitlab-cookbook-initial
gitlab-cookbook-rebaseline
$ cat .git/refs/tags/gitlab-cookbook-for-10.7.3
f16b12027cef7052e09f3a483ace55999800ea5b
#+END_SRC
- =HEAD=
#+BEGIN_SRC
$ cat .git/HEAD
ref: refs/heads/gitlab_10.x_upgrade
#+END_SRC
** Refs
*** Refs
- remotes
#+BEGIN_SRC
$ ls -1 .git/refs/remotes/origin/*
.git/refs/remotes/origin/ara_test
.git/refs/remotes/origin/brjones_aci_network
.git/refs/remotes/origin/gitlab_10.x_upgrade
.git/refs/remotes/origin/gitlab-ce-8.17
.git/refs/remotes/origin/gitlab-ce-9.1.4-defectFix
.git/refs/remotes/origin/HEAD
.git/refs/remotes/origin/master
$ cat .git/refs/tags/gitlab-cookbook-for-10.7.3
f16b12027cef7052e09f3a483ace55999800ea5b
#+END_SRC
- =HEAD=
#+BEGIN_SRC shell
$ cat .git/HEAD
ref: refs/heads/gitlab_10.x_upgrade
#+END_SRC
** Refs -- remotes
#+BEGIN_SRC shell
$ ls -1 .git/refs/remotes/origin/*
.git/refs/remotes/origin/ara_test
.git/refs/remotes/origin/brjones_aci_network
.git/refs/remotes/origin/gitlab_10.x_upgrade
.git/refs/remotes/origin/gitlab-ce-8.17
.git/refs/remotes/origin/gitlab-ce-9.1.4-defectFix
.git/refs/remotes/origin/HEAD
.git/refs/remotes/origin/master
$ cat .git/refs/remotes/origin/ara_test
7130b7ee374ad9f7ba784ec0b0d0b86dc99f41d4
#+END_SRC
$ cat .git/refs/remotes/origin/ara_test
7130b7ee374ad9f7ba784ec0b0d0b86dc99f41d4
#+END_SRC
** HEAD
*** HEAD
- =HEAD= is a ref that points to where the commit currently checked out
- =HEAD= in a remote repository usually points to the default branch
- =HEAD= is a ref that points to where the commit currently checked out
- =HEAD= in a remote repository usually points to the default branch
#+BEGIN_SRC
$ cat .git/HEAD
ref: refs/heads/master
$ cat .git/refs/remotes/origin/HEAD
ref: refs/remotes/origin/REL2_0
#+END_SRC
** Annotated tags
*** Annotated tags
- A normal tag is just a "ref", pointing to a commit.
#+BEGIN_SRC shell
git tag Rel1.0 Rel1
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)
#+END_SRC
- *Caveat*: tags and branches use different namespaces, so
temptation to tag the =Rel1= branch with =Rel1= would be
high. However, this causes confusion for many git tools, so
should be avoided.
** Annotated tags
*** Annotated tags
- An annotated tag is a separate git object, that records information specfic to the tag:
+ Tag name; date; tagger; commit it's pointing to
- Advice is for annotated tags to be used for significant announcements/releases/snaphots.
#+BEGIN_SRC shell
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)
#+END_SRC
#+BEGIN_SRC shell
$ cat .git/HEAD
ref: refs/heads/master
$ cat .git/refs/remotes/origin/HEAD
ref: refs/remotes/origin/REL2_0
#+END_SRC
** Annotated tags 1/2
- A normal tag is just a "ref", pointing to a commit.
#+BEGIN_SRC shell
git tag Rel1.0 Rel1
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)
#+END_SRC
- Caveat :: tags and branches use different namespaces, so
temptation to tag the =Rel1= branch with =Rel1= would be
high. However, this causes confusion for many git tools, so
should be avoided.
** Annotated tags 2/2
- An annotated tag is a separate git object, that records
information specfic to the tag:
+ Tag name; date; tagger; commit it's pointing to
- Advice is for annotated tags to be used for significant
announcements/releases/snaphots.
#+BEGIN_SRC shell
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)
#+END_SRC
** blame
*** =blame=
- Identifies the commit, commit author and date for each line in a file.
- Doesn't give information for lines that have been removed or replaced.
- Identifies the commit, commit author and date for each line in a
file.
- Doesn't give information for lines that have been removed or
replaced.
** Tag and commit signing
*** Tag and commit signing and verification
- PGP/GnuPG (=gpg=): expects familiarity with public/private key encryption.
- Sign tags and commits with private key to assure integrity
#+BEGIN_SRC shell
git commit -Seibhear.geo@gmail.com \
-m "Update to information.md"
git cat-file -p $(cat .git/refs/heads/master)
git tag -s -u eibhear.geo@gmail.com \
-m "Release 2." Rel2.0 Rel2
git cat-file -p $(cat .git/refs/tags/Rel2.0)
#+END_SRC
- Verify commits and tags with public key
#+BEGIN_SRC
git tag -v Rel2.0
git log --show-signature -1
#+END_SRC
- PGP/GnuPG (=gpg=): expects familiarity with public/private key encryption.
- Sign tags and commits with private key to assure integrity
#+BEGIN_SRC shell
git commit -Seibhear.geo@gmail.com -m \
"Update to information.md"
git cat-file -p $(cat .git/refs/heads/master)
git tag -s -u eibhear.geo@gmail.com -m "Release 2." Rel2.0 \
Rel2
git cat-file -p $(cat .git/refs/tags/Rel2.0)
#+END_SRC
- Verify commits and tags with public key
#+BEGIN_SRC shell
git tag -v Rel2.0
git log --show-signature -1
#+END_SRC
* The Continental shelf
**
*** Switch on the Sonar :B_block:BMCOL:
:PROPERTIES:
:BEAMER_col: 0.9
:BEAMER_env: block
:END:
file:./images/Loligo_vulgaris.jpg
#+latex: {\tiny
By © Hans Hillewaert, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=385705
#+latex: }
#+CAPTION: By © Hans Hillewaert, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=385705
#+ATTR_HTML: :width 70%
file:./images/Loligo_vulgaris.jpg
** Git Objects -- blobs
*** Blob (file)
A file
#+BEGIN_SRC shell
$ cat ~/.profile | git hash-object --stdin
c9db4591825bd7a918df686ff04aeb3a87d3bda0
#+END_SRC
- A file
#+BEGIN_SRC shell
$ cat ~/.profile | git hash-object \
--stdin
c9db4591825bd7a918df686ff04aeb3a87d3bda0
#+END_SRC
** Git Objects -- trees
*** Tree
A listing of files and other tree objects containing the
following information on each: access mode (similar to UNIX
permissions); type (e.g. =tree=, =blob=); SHA1; file/directory
name
#+BEGIN_SRC shell
$ git cat-file -p \
2c4e4782bcb6b13a0e11b6961004dec8745e9d35
040000 tree bcd2824258ddf007dae7f88da7d727fb3894691b
Astro
100644 blob 94aea57573b92d9188a3df4cf748b60efd968803
MyHelloWorldBean.java
100644 blob c55118d1afb2be6a6d0f728814c084d54e97db14
MyHelloWorldServlet.java
#+END_SRC
** Git Objects -- commits
*** Commit
Information on a commit event:
- The SHA1 of the top-level tree of the project.
- The parent commit (or commits, if this commit is the result of
a merge)
- The details of the author of the code that is being applied
with the commit (including date and time)
- The details of the person who applied the commit (including date and time)
- The commit gpg signature, if present
- The commit comment
** Git Objects -- commits
*** Commit
#+BEGIN_SRC shell
$ git cat-file -p \
37c5611a177c9eafbd17e4302b6d644434b1042b
tree 40b6262f3f3f5fc8cb8a0c78ca558a683dfc2323
parent 42608808a973b8e0c4a4b0105c2317d81b12851f
parent 36d56f097ca81f06d77f46cbde3fc10cbf6639f9
author Master O'Theuniverse \
<master.otheuniverse@example.com> \
1529840879 +0100
committer Master O'Theuniverse \
<master.otheuniverse@example.com> \
1529840879 +0100
- A listing of files and other tree objects containing the
following information on each: access mode (similar to UNIX
permissions); type (e.g. =tree=, =blob=); SHA1; file/directory
name
#+BEGIN_SRC shell
$ git cat-file -p 2c4e4782bcb6b13a0e11b6961004dec8745e9d35
040000 tree bcd2824258ddf007dae7f88da7d727fb3894691b Astro
100644 blob 94aea57573b92d9188a3df4cf748b60efd968803 MyHelloWorldBean.java
100644 blob c55118d1afb2be6a6d0f728814c084d54e97db14 MyHelloWorldServlet.java
#+END_SRC
** Git Objects -- commits 1/2
Information on a commit event:
- The SHA1 of the top-level tree of the project.
- The parent commit (or commits, if this commit is the result of a
merge)
- The details of the author of the code that is being applied with
the commit (including date and time)
- The details of the person who applied the commit (including date and time)
- The commit gpg signature, if present
- The commit comment
** Git Objects -- commits 2/2
#+BEGIN_SRC shell
$ git cat-file -p 37c5611a177c9eafbd17e4302b6d644434b1042b
tree 40b6262f3f3f5fc8cb8a0c78ca558a683dfc2323
parent 42608808a973b8e0c4a4b0105c2317d81b12851f
parent 36d56f097ca81f06d77f46cbde3fc10cbf6639f9
author Master O'Theuniverse <master.otheuniverse@example.com> 1529840879 +0100
committer Master O'Theuniverse <master.otheuniverse@example.com> 1529840879 +0100
REV18_5 now live
#+END_SRC
** Git Objects -- tags
*** Tag
A tag points to a commit object, and an annotated tag contains
additional information
- What object it's pointing at and its type
- The name of the tag
- Who applied the tag (including date and time)
- A tag comment
** Git Objects -- tags
*** Tag
#+BEGIN_SRC shell
$ git cat-file -p \
88a4c18867ccb1d7c398f285460d8abab3964e75
object 66d8336c2770d0d1cea3dcb0175611edb5e69f69
type commit
tag Rel1.0.a
tagger Éibhear Ó hAnluain \
<eibhear.geo@gmail.com> \
1529847749 +0100
REV18_5 now live
#+END_SRC
** Git Objects -- tags 1/2
A tag points to a commit object, and an annotated tag contains
additional information
- What object it's pointing at and its type
- The name of the tag
- Who applied the tag (including date and time)
- A tag comment
** Git Objects -- tags 2/2
#+BEGIN_SRC shell
$ git cat-file -p 88a4c18867ccb1d7c398f285460d8abab3964e75
object 66d8336c2770d0d1cea3dcb0175611edb5e69f69
type commit
tag Rel1.0.a
tagger Éibhear Ó hAnluain <eibhear.geo@gmail.com> 1529847749 +0100
An annotated tag for the Rel1 release
An annotated tag for the Rel1 release
$ git cat-file -t \
66d8336c2770d0d1cea3dcb0175611edb5e69f69
commit
#+END_SRC
$ git cat-file -t 66d8336c2770d0d1cea3dcb0175611edb5e69f69
commit
#+END_SRC
** "Content Addressable Filesystem"
*** "Content Addressable Filesystem"
As the IDs of objects are based on their contents, they are
located in the git database according to that name
#+BEGIN_SRC shell
git rev-list --all --objects
git cat-file -p \
b5aea839bc89a0c7931af469ff9c145be18854d7
git cat-file -p \
b5aea839bc89a0c7931af469ff9c145be18854d7 | \
git cat-file -p b5aea839bc89a0c7931af469ff9c145be18854d7
git cat-file -p b5aea839bc89a0c7931af469ff9c145be18854d7 | \
git hash-object --stdin
ls -l .git/objects/b5/aea839bc89a0c7931af469ff9c145be18854d7
#+END_SRC
* The Deep trenches
**
*** Exotic creatures :B_block:BMCOL:
:PROPERTIES:
:BEAMER_col: 0.7
:BEAMER_env: block
:END:
file:./images/Alvinella_pompejana01.jpg
* The Deep trenches -- Exotic creatures
#+latex: {\tiny
By National Science Foundation (University of Delaware College of Marine Studies) - http://www.nsf.gov/od/lpa/news/press/01/pr0190.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7123122
#+latex: }
#+CAPTION: By National Science Foundation (University of Delaware College of Marine Studies) - http://www.nsf.gov/od/lpa/news/press/01/pr0190.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=7123122
#+ATTR_HTML: :width 60%
file:./images/Alvinella_pompejana01.jpg
** The reflog
*** The reflog
- A log of all the changes to HEAD
- Local only: not involved in pulls, pushes or fetches.
- Useful for recovering accidentally removed commits
- Completely clear the reflog
: git reflog expire --expire=now \
: --expire-unreachable=now --verbose --all
- A log of all the changes to HEAD
- Local only: not involved in pulls, pushes or fetches.
- Useful for recovering accidentally removed commits
- Completely clear the reflog
#+BEGIN_SRC shell
git reflog expire --expire=now --expire-unreachable=now \
--verbose --all
#+END_SRC
** fsck and gc
*** fsck and gc
- fsck :: Analyse connectivity of the objects in the git
database. Useful for finding objects that aren't of any
use any more.
- gc :: "Garbage collector". Compress and pack objects, remove
"danlging" and unreachable objects
- fsck :: Analyse connectivity of the objects in the git
database. Useful for finding objects that aren't of any use any
more.
- gc :: "Garbage collector". Compress and pack objects, remove
"danlging" and unreachable objects
** Useful commands
*** Useful commands
- Find the largest object in your git database
#+BEGIN_SRC shell
git cat-file \
--batch-check='%(objecttype) %(objectname) %(objectsize)' \
--batch-all-objects | sed -n 's/^blob //p' | \
sort -n --key=2
#+END_SRC
- List all objects in your git database
: git rev-list --all --objects
- Determine the filename related to a blob object
: git rev-list --objects --all | grep <objectID>
- Determine commits that reference that file
: git log --follow -- "<fileNameAndPath>"
** Permanently removing a file from your git db
*** Permanently removing a file from your git db
- e.g. contains password information, v. large file not required, etc.
- For each branch...
+ Check it out
: git checkout <branch>
+ Remove the file from all commits
#+BEGIN_SRC shell
git filter-branch --tree-filter \
'rm -f <filePathAndName>' \
--prune-empty HEAD
#+END_SRC
+ Clean up the original refs
#+BEGIN_SRC shell
git for-each-ref --format="%(refname)" \
refs/original/ | \
xargs -n 1 git update-ref -d
#+END_SRC
** Permanently removing a file from your git db
*** Permanently removing a file from your git db
- ... then ...
- Clear out the reflog
: git reflog expire --expire-unreachable=now --all
The reflog maintains references to commits and objects you
may want to remove.
- Collect the garbage, regardless of age
: git gc --prune=now
- Sanity-check all objects
: git fsck --unreachable --no-reflogs
- Find the largest object in your git database
#+BEGIN_SRC shell
git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize)' \
--batch-all-objects | sed -n 's/^blob //p' | sort -n --key=2
#+END_SRC
- List all objects in your git database
#+BEGIN_SRC shell
git rev-list --all --objects
#+END_SRC
- Determine the filename related to a blob object
#+BEGIN_SRC shell
git rev-list --objects --all | grep <objectID>
#+END_SRC
- Determine commits that reference that file
#+BEGIN_SRC shell
git log --follow -- "<fileNameAndPath>"
#+END_SRC
** Permanently removing a file from your git db 1/2
- e.g. contains password information, v. large file not required, etc.
- For each branch...
+ Check it out
#+BEGIN_SRC shell
git checkout <branch>
#+END_SRC
+ Remove the file from all commits
#+BEGIN_SRC shell
git filter-branch --tree-filter \
'rm -f <filePathAndName>' --prune-empty HEAD
#+END_SRC
+ Clean up the original refs
#+BEGIN_SRC shell
git for-each-ref --format="%(refname)" refs/original/ | \
xargs -n 1 git update-ref -d
#+END_SRC
** Permanently removing a file from your git db 2/2
- ... then ...
- Clear out the reflog
#+BEGIN_SRC shell
git reflog expire --expire-unreachable=now --all
#+END_SRC
The reflog maintains references to commits and objects you may
want to remove.
- Collect the garbage, regardless of age
#+BEGIN_SRC shell
git gc --prune=now
#+END_SRC
- Sanity-check all objects
#+BEGIN_SRC shell
git fsck --unreachable --no-reflogs
#+END_SRC
** Other interesting concepts
*** Other interesting concepts
- *Porcelain vs Plumbing*: The commands that we use vs the commands that *they* use.
+ *Porcelain*: =init=, =clone=, =fetch=, =push=, =add=, =commit=, etc.
+ *Plumbing*: =hash-object=, =cat-file=, =write-tree=, =count-objects=, etc.
- *submodules*: to link a separate git repository into yours
- *fast-import*: to import data into a git repository from other,
non-git sources (e.g. cvs, subversion, etc.)
- Porcelain vs Plumbing :: The commands that we use vs the
commands that *they* use.
+ Porcelain :: =init=, =clone=, =fetch=, =push=, =add=,
=commit=, etc.
+ Plumbing :: =hash-object=, =cat-file=, =write-tree=,
=count-objects=, etc.
- submodules :: to link a separate git repository into yours
- fast-import :: to import data into a git repository from other,
non-git sources (e.g. cvs, subversion, etc.)
** Resources
*** Resources
- The git book :: https://git-scm.com/book/en/v2/
- The git manual ::
#+BEGIN_SRC shell
git help --all
git help merge
git help cat-file
man git-hash-object
#+END_SRC
- Stack overflow :: https://stackoverflow.com/questions/tagged/git
- The git book :: https://git-scm.com/book/en/v2/
- The git manual ::
#+BEGIN_SRC shell
git help --all
git help merge
git help cat-file
man git-hash-object
#+END_SRC
- Stack overflow :: https://stackoverflow.com/questions/tagged/git
* Commands :noexport:
| | add |
| | add--interactive |

5
styles/e-reveal.css
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@ -16,7 +16,6 @@ section {
pre,
code {
font-size: 80%;
color: #000000;
background-color: #e0e0e0;
border-style: solid;
@ -24,11 +23,13 @@ code {
border-color: #c0c0c0;
}
pre {
.org-src-container > pre {
padding: 0.5em;
font-size: 100%;
}
code {
font-size: 80%;
padding-right: 1px;
padding-left: 1px;
}