What is the difference between git merge and git merge --no-ff

Question

Using gitk log  I could not spot a difference between the two  How can I observe the difference  with a git command or some tool

User · Answer

The --no-ff option ensures that a fast forward merge will not happen  and that a new commit object will always be created  This can be desirable if you want git to maintain a history of feature branches    nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  nbsp  In the above image  the left side is an example of the git history after using git merge --no-ff and the right side is an example of using git merge where an ff merge was possible   EDIT  A previous version of this image indicated only a single parent for the merge commit  Merge commits have multiple parent commits which git uses to maintain a history of the  feature branch  and of the original branch  The multiple parent links are highlighted in green

User · Answer

Merge Strategies    Explicit Merge  Creates a new merge commit   This is what you will get if you used --no-ff      Fast Forward Merge  Forward rapidly  without creating a new commit       Rebase  Establish a new base level        Squash  Crush or squeeze  something  with force so that it becomes flat

User · Answer

Other answers indicate perfectly well that --no-ff results in a merge commit  This retains historical information about the feature branch which is useful since feature branches are regularly cleaned up and deleted  This answer may provide context for when to use or not to use --no-ff  Merging from feature into the main branch  use --no-ff Worked example    git checkout -b NewFeature  work   work   work    git commit -am   quot New feature complete  quot    git checkout main   git merge --no-ff NewFeature   git push origin main   git branch -d NewFeature  Merging changes from main into feature branch  leave off --no-ff Worked example    git checkout -b NewFeature  work   work   work   New changes made for HotFix in the main branch  Lets get them       git commit -am   quot New feature in progress quot    git pull origin main  shortcut for  quot git fetch origin main quot    quot git merge origin main quot

User · Answer

Graphic answer to this question  Here is a site with a clear explanation and graphical illustration of using git merge --no-ff     Until I saw this  I was completely lost with git  Using --no-ff allows someone reviewing history to clearly see the branch you checked out to work on   that link points to github s  network  visualization tool  And here is another great reference with illustrations  This reference complements the first one nicely with more of a focus on those less acquainted with git      Basic info for newbs like me  If you are like me  and not a Git-guru  my answer here describes handling the deletion of files from git s tracking without deleting them from the local filesystem  which seems poorly documented but often occurrence  Another newb situation is getting current code  which still manages to elude me     Example Workflow  I updated a package to my website and had to go back to my notes to see my workflow  I thought it useful to add an example to this answer    My workflow of git commands   git checkout -b contact-form  do your work on  contact-form   git status git commit -am   updated form in contact module  git checkout master git merge --no-ff contact-form git branch -d contact-form git push origin master   Below  actual usage  including explanations  Note  the output below is snipped  git is quite verbose     git status   On branch master   Changed but not updated       use  git add rm  lt file gt      to update what will be committed       use  git checkout --  lt file gt      to discard changes in working directory            modified    ecc Desktop php         modified    ecc Mobile php         deleted     ecc ecc-config php         modified    ecc readme txt         modified    ecc test php         deleted     passthru-adapter igs         deleted     shop mickey index php     Untracked files       use  git add  lt file gt      to include in what will be committed            ecc upgrade php         ecc webgility-config php         ecc webgility-config php bak         ecc webgility-magento php   Notice 3 things from above  1  In the output you can see the changes from the ECC package s upgrade  including the addition of new files  2  Also notice there are two files  not in the  ecc folder  I deleted independent of this change  Instead of confusing those file deletions with ecc  I ll make a different cleanup branch later to reflect those files  deletion  3  I didn t follow my workflow  I forgot about git while I was trying to get ecc working again    Below  rather than do the all-inclusive git commit -am  updated ecc package  I normally would  I only wanted to add the files in the  ecc folder  Those deleted files weren t specifically part of my git add  but because they already were tracked in git  I need to remove them from this branch s commit     git checkout -b ecc   git add ecc     git reset HEAD passthru-adapter igs   git reset HEAD shop mickey index php Unstaged changes after reset  M       passthru-adapter igs M       shop mickey index php    git commit -m  Webgility ecc desktop connector files  integrates with Quickbooks     git checkout master D       passthru-adapter igs D       shop mickey index php Switched to branch  master    git merge --no-ff ecc   git branch -d ecc Deleted branch ecc  was 98269a2     git push origin master Counting objects  22  done  Delta compression using up to 4 threads  Compressing objects  100   14 14   done  Writing objects  100   14 14   59 00 KiB  done  Total 14  delta 10   reused 0  delta 0  To git github com me mywebsite git    8a0d9ec  333eff5  master - gt  master      Script for automating the above  Having used this process 10  times in a day  I have taken to writing batch scripts to execute the commands  so I made an almost-proper git update sh  lt branch gt   lt  commit message  gt  script for doing the above steps  Here is the Gist source for that script    Instead of git commit -am I am selecting files from the  modified  list produced via git status and then pasting those in this script  This came about because I made dozens of edits but wanted varied branch names to help group the changes

User · Answer

The --no-ff flag causes the merge to always create a new commit object  even if the merge could be performed with a fast-forward  This avoids losing information about the historical existence of a feature branch and groups together all commits that together added the feature

User · Answer

The --no-ff flag prevents git merge from executing a  fast-forward  if it detects that your current HEAD is an ancestor of the commit you re trying to merge  A fast-forward is when  instead of constructing a merge commit  git just moves your branch pointer to point at the incoming commit  This commonly occurs when doing a git pull without any local changes   However  occasionally you want to prevent this behavior from happening  typically because you want to maintain a specific branch topology  e g  you re merging in a topic branch and you want to ensure it looks that way when reading history   In order to do that  you can pass the --no-ff flag and git merge will always construct a merge instead of fast-forwarding   Similarly  if you want to execute a git pull or use git merge in order to explicitly fast-forward  and you want to bail out if it can t fast-forward  then you can use the --ff-only flag  This way you can regularly do something like git pull --ff-only without thinking  and then if it errors out you can go back and decide if you want to merge or rebase

User · Answer

This is an old question  and this is somewhat subtly mentioned in the other posts  but the explanation that made this click for me is that non fast forward merges will require a separate commit

[git] What is the difference between `git merge` and `git merge --no-ff`?

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