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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
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GitDeepDive.org
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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=
@ -196,24 +198,16 @@
#+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
#+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
@ -223,10 +217,9 @@
$ cat .git/refs/heads/gitlab-ce-8.17
c63767d0b9b520f36a533237624dfaa1256b463c
#+END_SRC
** Refs
*** Refs
** Refs -- tags
- tags
#+BEGIN_SRC
#+BEGIN_SRC shell
$ ls -1 .git/refs/tags/
gitlab-cookbook-for-10.7.3
gitlab-cookbook-initial
@ -236,14 +229,12 @@
f16b12027cef7052e09f3a483ace55999800ea5b
#+END_SRC
- =HEAD=
#+BEGIN_SRC
#+BEGIN_SRC shell
$ cat .git/HEAD
ref: refs/heads/gitlab_10.x_upgrade
#+END_SRC
** Refs
*** Refs
- remotes
#+BEGIN_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
@ -257,18 +248,16 @@
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
#+BEGIN_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
*** Annotated tags
** Annotated tags 1/2
- A normal tag is just a "ref", pointing to a commit.
#+BEGIN_SRC shell
git tag Rel1.0 Rel1
@ -276,226 +265,199 @@
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
- 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:
** 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.
- 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
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 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 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
#+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
- A file
#+BEGIN_SRC shell
$ cat ~/.profile | git hash-object --stdin
$ cat ~/.profile | git hash-object \
--stdin
c9db4591825bd7a918df686ff04aeb3a87d3bda0
#+END_SRC
** Git Objects -- trees
*** Tree
A listing of files and other tree objects containing the
- 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
$ 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
** 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 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
** Git Objects -- commits 2/2
#+BEGIN_SRC shell
$ git cat-file -p \
37c5611a177c9eafbd17e4302b6d644434b1042b
$ 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
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
** 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
*** Tag
** Git Objects -- tags 2/2
#+BEGIN_SRC shell
$ git cat-file -p \
88a4c18867ccb1d7c398f285460d8abab3964e75
$ git cat-file -p 88a4c18867ccb1d7c398f285460d8abab3964e75
object 66d8336c2770d0d1cea3dcb0175611edb5e69f69
type commit
tag Rel1.0.a
tagger Éibhear Ó hAnluain \
<eibhear.geo@gmail.com> \
1529847749 +0100
tagger Éibhear Ó hAnluain <eibhear.geo@gmail.com> 1529847749 +0100
An annotated tag for the Rel1 release
$ git cat-file -t \
66d8336c2770d0d1cea3dcb0175611edb5e69f69
$ 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
#+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.
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
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
#+BEGIN_SRC shell
git rev-list --all --objects
#+END_SRC
- Determine the filename related to a blob object
: git rev-list --objects --all | grep <objectID>
#+BEGIN_SRC shell
git rev-list --objects --all | grep <objectID>
#+END_SRC
- 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
#+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
: git checkout <branch>
#+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
'rm -f <filePathAndName>' --prune-empty HEAD
#+END_SRC
+ Clean up the original refs
#+BEGIN_SRC shell
git for-each-ref --format="%(refname)" \
refs/original/ | \
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
** Permanently removing a file from your git db 2/2
- ... 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.
#+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
: git gc --prune=now
#+BEGIN_SRC shell
git gc --prune=now
#+END_SRC
- Sanity-check all objects
: git fsck --unreachable --no-reflogs
#+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,
- 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

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;
}