Fast-Forward Merge

Fast-Forward Merge

A fast-forward merge happens when Git can simply move the branch pointer forward because there’s a direct linear path between the branches.

Visual Example

Before merge:

git_2:      A---B---C
                     git_1:                D---E---F

If you’re on git_2 and merge git_1, Git sees that git_2 hasn’t diverged - it just hasn’t caught up yet. So Git simply moves the git_2 pointer forward to F:

After fast-forward merge:

git_2:      A---B---C---D---E---F
git_1:                          ↑
                           (both here)

No merge commit is created - the history stays linear.

When Fast-Forward is NOT Possible

Before merge:

            A---B---C---D  (git_2)
                                   E---F    (git_1)

Here both branches have diverged (both have new commits). Git cannot fast-forward, so it creates a merge commit:

After regular merge:

            A---B---C---D---M  (git_2)
                          /
                  E---F----    (git_1)

The --no-ff Flag

Even when fast-forward is possible, --no-ff forces Git to create a merge commit, preserving the fact that work happened on a separate branch:

            A---B---C-------M  (git_2)
                          /
                      D---E    (git_1)

This is useful for maintaining clear branch history in your repository.