Git fast-forward Merge:
1) 'dev' branch is created from the parent ‘master’ branch and current HEAD is at 'dev' branch which has active development changes.
2) After 'dev' branch changes are completed we are required to merge the changes back to parent branch ‘master’.
3) We run the command, $ git merge dev, allowing all changes from dev to be merged into master. Here no actual merge happens instead the HEAD pointer which is pointing to master (base code of dev), the HEAD is moved from earlier version to latest on tip of dev branch.
Git Three-way Merge (Recursive Merge):
1) There are two branches 'master' and 'dev' with 'dev' as child branch of 'master'. Here both 'dev' and 'master' branches have progressed ahead after the 'dev' branch is created.
2) Now we want to merge the branch 'dev' with 'master', as branch 'master' has progressed ahead after the last merge with 'dev' base code hash, fast-forward merge will not work, instead, git performs three-stage comparison and the results are as shown below.
GIT Rebase operation:
1) Consider we have below branch structure. Dev is the main development branch with rel-1.0 and rel-2.0 as parallel branches with same base branch.
2) As the rel-1.0 approaches deployment (prod release), rel-1.0 branch is merged to 'dev' (parent branch). This is going to be a fast-forward merge.
3) After rel-1.0 is complete, we can delete the branch rel-1.0 and the new code in production ('dev'/'master' branch) should become the new base for rel-2.0. Now this can be done using the rebase command, which works in a very different way than a Merge.
Move/ switch to rel-2.0 branch and run command,
$ git rebase dev
4) After we run the rebase command, HEAD moved to the tip of dev branch.
5) All commits in rel-2.0 branch after the common base is detached and moved on top of current tip of dev branch.
While working with rebasing, there’s a possibility of conflict. Now to resolve the conflict, we edit the file in conflict and run git add command and then use $ git rebase-continue command.
Below is the screen capture of $ git rebase command.
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