Rebase vs. Merge: Integrating Changes in Git

This article continues our "Advanced Git" series. Follow us on Twitter or subscribe to our newsletter for updates on future articles!

Effective Git branching is crucial for developers. My previous article detailed branching strategies, Git's branching model, branch types, and common workflows. The core benefit: isolated workspaces (branches) significantly improve version control.

This article focuses on integrating branches – efficiently merging code back into the main development line. We'll explore two key methods: merging and rebasing.

Both git merge and git rebase solve the same problem: integrating changes from one branch into another. However, their approaches differ significantly. Let's examine merging first.

Advanced Git Series:

• Part 1: Crafting the Ideal Git Commit
• Part 2: Optimizing Git Branching Strategies
• Part 3: Streamlining Collaboration with Pull Requests
• Part 4: Resolving Merge Conflicts Effectively
• Part 5: Rebase vs. Merge (You are here!)
• Part 6: Mastering Interactive Rebase
• Part 7: Cherry-Picking Commits in Git
• Part 8: Utilizing the Reflog to Recover Lost Commits

Understanding Git Merges

The git merge command integrates branches. Imagine branch-B with new commits; to merge into branch-A:

<code>$ git checkout branch-A
$ git merge branch-B</code>

This creates a new merge commit on branch-A, connecting both branch histories. Git identifies three key commits:

• The common ancestor: The point where both branches shared identical code before diverging.
• The branch endpoints: The latest commits on each branch, representing their current states.

Git combines these commits to achieve integration. A simplified scenario (where branch-A has no commits since branching) results in a "fast-forward" merge – efficiently adding branch-B's commits directly.

However, in most real-world scenarios, both branches have evolved independently. Git then creates a merge commit to combine the changes, a distinct commit automatically generated, unlike developer-created commits. Understanding this automatic merge requires analyzing the complete branch histories.

Human vs. Merge Commits

Developer-created commits are carefully structured, containing related changes and informative messages. Merge commits, conversely, automatically connect branches, not necessarily representing a semantically coherent set of changes.

Integrating with Rebasing

Rebasing offers an alternative to merging. It's not inherently "better," just different. You can successfully manage Git solely with merging. However, understanding rebasing provides valuable options.

Rebasing avoids automatic merge commits, creating a linear project history, eliminating branch divergence traces.

Rebasing: A Step-by-Step Guide

Let's rebase branch-B into branch-A:

<code>$ git checkout branch-A
$ git rebase branch-B</code>

The process involves three steps:

1. Temporarily removing commits: Commits on branch-A after the common ancestor are temporarily stored.
2. Applying branch-B's commits: branch-B's commits are applied, temporarily aligning both branches.
3. Rebasing branch-A's commits: The temporarily stored branch-A commits are reapplied on top of branch-B's commits, creating a linear history.

The result: a streamlined history without merge commits.

Rebasing's Potential Pitfalls

Crucially, rebasing rewrites commit history. While the content remains the same, the commit's parent changes, generating a new SHA-1 hash.

This is acceptable for unpublished commits. However, rebasing published commits is risky, potentially disrupting collaborators who based their work on the original commits.

The golden rule: Never rebase public branches! Use rebasing locally to clean up your history before integrating into shared branches.

Integration Strategies: Merge vs. Rebase

Merging and rebasing are both valuable tools. Merging preserves history non-destructively. Rebasing streamlines history but requires caution regarding published commits.

Explore my free "Advanced Git Kit" for deeper insights into Git tools.

Happy merging and rebasing! See you in the next "Advanced Git" installment!

Advanced Git Series:

• Part 1: Crafting the Ideal Git Commit
• Part 2: Optimizing Git Branching Strategies
• Part 3: Streamlining Collaboration with Pull Requests
• Part 4: Resolving Merge Conflicts Effectively
• Part 5: Rebase vs. Merge (You are here!)
• Part 6: Mastering Interactive Rebase
• Part 7: Cherry-Picking Commits in Git
• Part 8: Utilizing the Reflog to Recover Lost Commits

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