Advanced Branch Integration: Git Rebasing

Advanced Git

Amanda Crawford-Adamo

Software and Data Engineer

Git rebase

Method to integrate changes
Different from merge
Removes merge commits for a cleaner history
Maintains a linear commit graph for clarity

Git Rebase Command:

git rebase <branch_name>

Rebase example - before

An image of the data cleanup feature branch and main branch. The feature branch diverges after the second commit in main. The main branch has two additional commits after the data cleanup branch was created.

Rebase process

Checkout your data-cleanup feature branch.

git checkout data-cleanup

Rebase main branch onto data-cleanup branch.

git rebase main

data-cleanup commits are recreated after main's latest commit

Rebased data-cleanup commits get new hashes

Note: If there are any conflicts, these would need to be resolved manually.

Rebase example - after

An image of the data cleanup branch rebased onto the main branch. The data cleanup branch now all of main branch commits and the data cleanup commits now begin after all of main commits. Main branch has not changed.

Interactive rebase

git rebase -i <commit_hash>

Functionality

Allows developer to make granular changes to multiple commits
Opens an editor

Warning!

Rebasing public branches can disrupt workflows
- Do not use rebase on public branches, like main
Establish team rules on when to use rebase

Interactive rebase - before

Here is the data-validation branch history before we edit the commit history.

$ git log --oneline data-validation
abc1234 Optimize validation performance
def5678 Fix validation bug
ghi9101 Add data validation function
xyz1234 New Main Branch Commit
vwx7890 Main Branch Commit
jkl2345 Initial commit

Interactive rebase editor

Here's how we edit the commit history using pick and fixup commands in the open editor.

$ git rebase -i HEAD~3 
pick ghi9101 Add data validation function
fixup def5678 Fix validation bug
fixup abc1234 Optimize validation performance

# Rebase xyz1234..abc1234 onto HEAD~3(xyz1234) (3 commands)
#
# Commands:
# p, pick <commit> = use commit
# f, fixup <commit> = like "squash", but discard this commit's log message
...

Interactive rebase - after

Before

$ git log --oneline data-validation
abc1234 Optimize validation performance
def5678 Fix validation bug
ghi9101 Add data validation function
xyz1234 New Main Branch Commit
vwx7890 Main Branch Commit
jkl2345 Initial commit

After

$ git log --oneline data-validatoin
mno6789 Add data validation function
xyz1234 New Main Branch Commit
vwx7890 Main Branch Commit
jkl2345 Initial commit

The following commits are combined into one

abc1234
def5678
ghi9101

Merge versus rebase

The image shows three graphs, a diverged branch graph, the resulting merge graph, and the resulting rebased graph

Merge

Preserves full history and branch structure
Maintains context of parallel development

Rebase

Replays commits on top of the target branch
Creates a linear history
Loses some contextual information

When to use merge versus rebase

Merge

For integrating completed features, preserving development context

Rebase

For keeping feature branches updated with main, or for cleaning up before merging

Remember

Rebase rewrites history - use it carefully

Let's practice!

Advanced Git