These are the slides that I presented at XP Days Ukraine on Nov 10, 2017.

1. $ git anti-patterns
how to mess up with git
and love it again
LEMi ORHAN ERGiN
Agile Software Craftsman, iyzico
/lemiorhan
@lemiorhan
lemiorhanergin.com
bit.ly/lemiorhan

2. /lemiorhan
lemiorhanergin.com
@lemiorhan
LEMi ORHAN ERGiN
agile software craftsman @ iyzico
ex-Sony, ex-eBay
founder of Turkish Software Craftsmanship Community

3. git is powerful
but you have to know using it properly
because of its internal structure

4. Are you using git
if all you do is commit-push-pull
use dropbox instead
ANTIPATTERN DANGER
as if it is dropbox ?
1DROPBOX-ISH GIT ANTI-PATTERN

5. learn
no worries, I will cover how git behaves in 5 minutes
git works
how

6. the way it keeps
FILES & FOLDERS
.git folder, aka repository
working copy
staging area
objects database
the way it keeps
REFERENCES
directed acyclic graph
keeping snapshots
traversing graph
branches, tags, heads
git has 2 mechanisms

7. Source Code
Working Copy
you want to version changes

8. Source Code
Working Copy
$ git init
Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
initializing repo

9. Source Code
Working Copy
$ git init --bare
Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
initializing bare repo

10. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git add .
preparing commits

11. folder
folder
folder
file
file
file
$ git add .
preparing commits

12. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git add .
preparing commits

13. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git commit -m “initial commit”
commi!ing

14. $ git commit -m “initial commit”
commi!ing
folder
folder
folder
file
file
file
commit
branch
HEAD
For more details, refer to book
Git Internals by Scott Chacon

15. folder
folder
folder
file
file
file
commit
$ git commit -m “second commit”
commi!ing
folder
commit
branch
HEAD
folder
file
folder
For more details, refer to book
Git Internals by Scott Chacon

16. folder
folder
folder
file
file
file
commit
$ git commit -m “third commit”
commi!ing
folder
commit
folder
file
folder
folder
commit
branch
HEAD
file
For more details, refer to book
Git Internals by Scott Chacon

17. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git commit -m “initial commit”
commi!ing

18. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git remote add origin http://upstream.repo
$ git push -u origin master pushing to remote

19. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
new changes from others are pushed

20. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git fetch
fetching changes

21. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git merge FETCHED_HEAD
updating working copy

22. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git pull
git fetch + git merge
ge!ing changes to source code

23. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
want to update last commit

24. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git reset --soft $ git commit --amend/ so" reseting
cannot be reached
Only the cache for
the commit you reseted
is removed from staging area
for your current branch

25. folder
folder
folder
file
file
file
commit
folder
commit
folder
file
folder
folder
commit
branch
HEAD
file
For more details, refer to book
Git Internals by Scott Chacon
$ git reset --soft $ git commit --amend/ so" reseting

26. folder
folder
folder
file
file
file
commit
folder
commit
folder
file
folder
folder
commit
branch
HEAD
file
For more details, refer to book
Git Internals by Scott Chacon
$ git reset --soft $ git commit --amend/ so" reseting

27. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
want to squash or change last commits

28. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git reset --mixed
mixed reseting
cannot be reached
entries for commits, files
and folders are removed
from staging area

29. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
want to get rid of last commits

30. Object Database
.git Folder / Object Database
Cache
Staging Area / The Index
Remote
Upstream Repo / Remote Repo
Server
Source Code
Working Copy
$ git reset --hard
hard reseting
cannot be reached
removed from staging area
removed from working copy

31. are you brave enough to
jump to any commit ?
jump to a branch
create a branch from a commit
create a branch from a tag
ANTIPATTERN DANGER
$ git checkout feature/PA-121
$ git checkout -b fix/missing-sign-parameter 2449be8
$ git checkout -b hotfix/v1.1 tags/v1
2BROKEN TIME MACHINE ANTI-PATTERN

32. are you sure?
are you brave enough to
jump to any commit ?

33. do you have
loooooong living
topic branches ?
ANTIPATTERN DANGER
3LONG LIVING BRANCHES ANTI-PATTERN

34. do you have
loooooong living
topic branches ?
welcome to
merge hell

35. before merging
do you validate commits
back to source ?
ANTIPATTERN DANGER
code review, continuous integration, automated testing…
4TOO LATE TO VALIDATE ANTI-PATTERN

36. before merging
do you validate commits
back to source ? areyou
sure?

37. merge and unmerge
do you o!en need to
just before releases ?
ANTIPATTERN DANGER
5CHERRY-PICK OBSSESSION ANTI-PATTERN

38. merge and unmerge
do you o!en need to
just before releases ?
master
HEAD
TAG/v13
version 14
$ git cherry-pick Every-Single-Commit-We-Want-To-Deploy

39. the commit graph ?
do you fully understand
ANTIPATTERN DANGER
6DEATH ON COMMIT GRAPH ANTI-PATTERN

40. the commit graph ?
do you fully understand
topic and shared branches, tracking branches, tags, HEADs, merge commits, reverted commits…

41. Cure?

42. Commit Early, Commit O"en
Perfect Later, Publish Once

43. STEP 0
split your big feature into
mini shippable tasks
master
HEAD
TOPIC
ORIGIN/master
refactorings
tasks, like rest endpoints
red-green-refactor
each task will have a
branch, not a feature

44. STEP 1
commit early
commit o!en
no need to compile
no need for CI
it’s only for versioning
do not push
master
HEAD
TOPIC
ORIGIN/master

45. always pull with rebase
$ git pull --rebase origin master
to get forced pushes securely
to rebase your commits
master
HEAD
TOPIC
STEP 2
ORIGIN/master
and do it o!en!

46. $ git pull --rebase origin master
master
HEAD
TOPIC
STEP 2
ORIGIN/master
always pull with rebase
to get forced pushes securely
to rebase your commits
and do it o!en!

47. $ git pull --rebase origin master
master
HEAD
TOPIC
STEP 2
ORIGIN/master
if you branch is pushed already
$ git push -f
always pull with rebase
to get forced pushes securely
to rebase your commits
and do it o!en!

48. $ git pull --rebase origin master
master
HEAD
TOPIC
STEP 2
ORIGIN/master
if you branch is pushed already
$ git push -f
Sync source branch a!erwards
$ git fetch origin master:master
always pull with rebase
to get forced pushes securely
to rebase your commits
and do it o!en!

49. perfect later
make it single commit
$ git reset HEAD~3
$ git rebase -i HEAD~3
$ git merge --squash
HEAD
TOPIC
STEP 3
ORIGIN/master
tests are passing
app is working
code is reviewed (*)
master

50. HEAD
TOPIC
STEP 3
ORIGIN/master
perfect later
make it single commit
tests are passing
app is working
code is reviewed (*)
master
$ git reset HEAD~3
$ git rebase -i HEAD~3
$ git merge --squash

51. Use feature flags/toggles
HEAD
TOPIC
STEP 4
ORIGIN/master
if feature should be disabled
merge back to source
$ git checkout master
$ git merge topic
master

52. Use feature flags/toggles
master
HEAD
TOPIC
STEP 4
ORIGIN/master
if feature should be disabled
merge back to source
$ git checkout master
$ git merge topic

53. Continuous Integration
validates master branch
continuouslymaster
HEAD
TOPIC
ORIGIN/master
Pull requests can be
used to review code
and to validate before
merging back to master
Scrum tasks are
mapped to commits,
not stories
Github Flow can be
used to govern overall
TRUNK-BASED
DEVELOPMENT
let's make git great again
Feature flags should be
used whenever possible
Commit early & o"en
perfect later, publish
once philosophy
Deliver frequently
be prepared to send
every single commit
Deleting branches a"er
merge will make your
commit graph readable

54. use terminal
GUIs are prison balls of developers
it’s ok to use GUIs while checking diffs,
resolving conflicts and viewing commit graph
BUTTON ADDICT ANTI-PATTERN
7
ANTIPATTERN DANGER

55. stop adding
prevent commits from being big ball of muds
every change
OMNIBUS BILL ANTI-PATTERN
8
ANTIPATTERN DANGER

56. stop adding
prevent commits from being big ball of muds
every change
local change sets at JetBrains IDEs

57. stop adding every change
partial add

58. messages
are
read!
# WHAT
# <issue id> (this commit will...) <subject>
# WHY and HOW
# Explain why this change is being made
# RELATED
# Provide links or keys to any relevant issues or other resources
# REMEMBER
# use lower case in the subject line
# start with a verb in imperative tone in the subject line
# do not end the subject line with a period
# separate subject from body with a blank line
# use the body to explain what and why vs. how
# can use multiple lines with "-" for bullet points in body
$ git config --global commit.template ~/.git-commit-template.txt
$ git config --global commit.cleanup strip
use git commit
templates to
create be"er
commit messages
comtmi
F*CKING COMMIT MESSAGES ANTI-PATTERN
9
ANTIPATTERN DANGER

59. messages
are
read!
use git commit
templates to
create be"er
commit messages
comtmi

60. ANTIPATTERN DANGER
10ZOMBIE REBASE ANTI-PATTERN
Rebase Conflicts
Death by
master
HEAD
TOPIC

61. TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6
git:(topic) $ git rebase master
rebase
how
really works
command

62. TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6
git:(topic) $ git rebase master
rebase
how
really works
command

63. TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6
git:(topic) $ git rebase master
rebase
how
really works
command

64. TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6 c5'
REPLAY #1
git:(topic) $ git rebase master
orig_HEAD
rebase
how
really works
command

65. TOPIC
master
c1 c2 c3 c4 c7
c5 c6c5 c6 c5' c6c6'
git:(topic) $ git rebase master
HEAD
REPLAY #2
orig_HEAD
rebase
how
really works
command

66. TOPIC
master
c1 c2 c3 c4 c7
HEAD
c5 c6c5 c6 c5' c6c6'
git:(topic) $ git rebase master
REWIND
orig_HEAD
rebase
how
really works
command

67. master
c1 c2 c3 c4 c7
c5' c6c6'
git:(topic) $ git rebase master
TOPIC
HEAD
REWIND
rebase
how
really works
command

68. master
HEAD
TOPIC
YOU STILL WANT TO REBASE, RIGHT?

69. master
HEAD
TOPIC
$ git merge topicmerge to branches:
merge with squash:
squash and rebase:
$ git merge topic --squash
$ git reset HEAD~8
$ git commit
$ git rebase master

70. 1. DROPBOX-ISH GIT
2. BROKEN TIME MACHINE
3. LONG LIVING BRANCHES
4. TOO LATE TO VALIDATE
5. CHERRY-PICK OBSSESSION
6. DEATH ON COMMIT GRAPH
7. BUTTON ADDICT
8. TRASH HOUSE
9. OMNIBUS BILL
10. F*CKING COMMIT MESSAGES
11. ZOMBIE REBASE
12. CODE LOSING SYNDROME
13. MESS UP WITH THE ROLLBACK
14. CENTRALIZED GIT
15. MERGE FANATIC
16. BRANCH CEMETERY
17. UNCONTROLLED POWER
18. WEB OF REPOSITORIES
19. ORACLE SYNDROME
20. WAITING FOR HACKERS
21. EVIL MERGE
22. BRANCH OVERDOSE
23. CHUCKY THE COMMAND
24. NO HERO TO SAVE LIVES
25. DUPLICATE COMMITS
26. BIG FAT COMMIT
27. CONFLICT-FOBIA
28. LIVING AT DETACHED HEAD STATE

71. RECAP
what was really
happened at that time?
LET’S

72. master
TAG/v1.1
login
HEAD
DETACHED HEAD STATE
$ git checkout cecd95914
Note: checking out 'cecd95914'.
You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by performing another checkout.
LIVING AT DETACHED HEAD STATE ANTI-PATTERN
11
ANTIPATTERN DANGER

73. master
TAG/v1.1
login
DETACHED HEAD STATE
$ git rebase (and conflicts happen)
$ git checkout HEAD~2
$ git checkout 43e3ab01
$ git checkout tags/v1.1
WHEN IT HAPPENS
HEAD

74. master
TAG/v1.1
login
HEAD
poor little developer...

75. master
TAG/v1.1
login
HEAD
$ git checkout master

76. master
TAG/v1.1
login
HEAD
$ git reflog
aa67e3a2c HEAD@{0}: rebase finished: returning to refs/heads/fix/java-sql-Date-violates-LSR
aa67e3a2c HEAD@{1}: rebase: fixes UnsupportedOperationException while calling toIstant() method of java.sql.Date
a45f3c4e5 HEAD@{2}: rebase: checkout develop
630ddad6e HEAD@{3}: checkout: moving from develop to fix/java-sql-Date-violates-LSR
b26cf7a1a HEAD@{4}: rebase: checkout develop
630ddad6e HEAD@{5}: checkout: moving from develop to fix/java-sql-Date-violates-LSR
b26cf7a1a HEAD@{6}: pull: Fast-forward
8b59f8f50 HEAD@{7}: checkout: moving from fix/java-sql-Date-violates-LSR to develop

77. $ git reflog
630ddad6e
the one we are
searching for
master
TAG/v1.1
login
HEAD
aa67e3a2c HEAD@{0}: rebase finished: returning to refs/heads/fix/java-sql-Date-violates-LSR
aa67e3a2c HEAD@{1}: rebase: fixes UnsupportedOperationException while calling toIstant() method of java.sql.Date
a45f3c4e5 HEAD@{2}: rebase: checkout develop
630ddad6e HEAD@{3}: checkout: moving from develop to fix/java-sql-Date-violates-LSR
b26cf7a1a HEAD@{4}: rebase: checkout develop
630ddad6e HEAD@{5}: checkout: moving from develop to fix/java-sql-Date-violates-LSR
b26cf7a1a HEAD@{6}: pull: Fast-forward
8b59f8f50 HEAD@{7}: checkout: moving from fix/java-sql-Date-violates-LSR to develop

78. master
typofix
TAG/v1.1
login
HEAD
$ git branch typofix 630ddad6e

79. master
typofix
TAG/v1.1
login
HEAD
$ git branch typofix 630ddad6e
KEEP CALM, NOTHING WILL BE LOST

80. LEMi ORHAN ERGiN
agile software craftsman @ iyzico
/lemiorhan
lemiorhanergin.com
@lemiorhan
ANTIPATTERN DANGER
thank you all!
Feedback: bit.ly/lemiorhan