Git fast forward VS no fast forward merge
Git merge allow us to perform fast forward and no fast fast forward branch merging. Any ideas when to use fast forward merge and when to use no fast forward merge?
The --no-ff option is useful when you want to have a clear notion of your feature branch. So even if in the meantime no commits were made, FF is possible - you still want sometimes to have each commit in the mainline correspond to one feature. So you treat a feature branch with a bunch of commits as a single unit, and merge them as a single unit. It is clear from your history when you do feature branch merging with --no-ff .
If you do not care about such thing - you could probably get away with FF whenever it is possible. Thus you will have more svn-like feeling of workflow.
For example, the author of this article thinks that --no-ff option should be default and his reasoning is close to that I outlined above:
Consider the situation where a series of minor commits on the "feature" branch collectively make up one new feature: If you just do "git merge feature_branch" without --no-ff , "it is impossible to see from the Git history which of the commit objects together have implemented a feature—you would have to manually read all the log messages. Reverting a whole feature (ie a group of commits), is a true headache [if --no-ff is not used], whereas it is easily done if the --no-ff flag was used [because it's just one commit]."
I can give an example commonly seen in project.
Here, option --no-ff (ie true merge) creates a new commit with multiple parents, and provides a better history tracking. Otherwise, --ff (ie fast-forward merge) is by default.
$ git checkout master
$ git checkout -b newFeature
$ ...
$ git commit -m 'work from day 1'
$ ...
$ git commit -m 'work from day 2'
$ ...
$ git commit -m 'finish the feature'
$ git checkout master
$ git merge --no-ff newFeature -m 'add new feature'
$ git log
// something like below
commit 'add new feature' // => commit created at merge with proper message
commit 'finish the feature'
commit 'work from day 2'
commit 'work from day 1'
$ gitk // => see details with graph
$ git checkout -b anotherFeature // => create a new branch (*)
$ ...
$ git commit -m 'work from day 3'
$ ...
$ git commit -m 'work from day 4'
$ ...
$ git commit -m 'finish another feature'
$ git checkout master
$ git merge anotherFeature // --ff is by default, message will be ignored
$ git log
// something like below
commit 'work from day 4'
commit 'work from day 3'
commit 'add new feature'
commit 'finish the feature'
commit ...
$ gitk // => see details with graph
(*) Note that here if the newFeature branch is re-used, instead of creating a new branch, git will have to do a --no-ff merge anyway. This means fast forward merge is not always eligible.
It is possible also that one may want to have personalized feature branches where code is just placed at the end of day. That permits to track development in finer detail.
I would not want to pollute master development with non-working code, thus doing --no-ff may just be what one is looking for.
As a side note, it may not be necessary to commit working code on a personalized branch, since history can be rewritten git rebase -i and forced on the server as long as nobody else is working on that same branch.
上一篇: 默认转发合并？
下一篇: Git快进VS没有快进合并